The tendency of immortals in fantasy and science fiction to not act significantly older than they look — even if they're Really 700 Years Old.
Fair enough when you're talking about an alien species or fantasy race with a very long lifespan. Ancient vampires who behave like teenagers — or even like ordinary adults — may present more of a strain on credibility, relative to the seriousness of the genre in which they appear.
Often justified in the sense that an immortal wouldn't have to deal with many of the psychological aspects of growing older. Their bodies don't break down with age, so they don't have to come to terms with decreased mobility or mental capacity. They won't die of natural causes, so they don't have to contemplate the inevitability of death, or the possibility of an eternal reward (or punishment) and all the moral responsibility that might carry. They don't have to worry about their legacy or leaving anything unfinished, because there really is always tomorrow. They don't take on the responsibilities of parenthood, because the species survives without the need for each member of the population to produce and care for its replacements. Because of all this, these characters never need to "grow up" in the sense that a mortal does. It could also be down to the creators themselves simply having no idea how the psychology of a centuries-old being ought to be.
A darker take of this would be where the immaturity is a facade, and the character does indeed have inner angsts and turmoils that most mortals actually wouldn't be able to relate to. For example, being immortal but having mortal friends would mean watching them age and eventually perish while you remain unchanged, and while you wouldn't have to wonder about what awaits you in the afterlife, the question of what will happen to you when the world ends and there are no more people remains. Thus, inner angst is generated over stuff that mortals don't have to worry about, but is kept hidden except for special circumstances when the immortal character gets the spotlight, when such issues are thrown into light for for Hidden Depths or Character Development.
There is an argument to be made that absent changes to the body, the rate of 'change' to the mind slows even in real life; that is, the changes between birth and age 10 are vastly bigger than the changes from 10 to 20, which in turn are much larger than the difference between 20 and 40 or even 20 and 60. This argument would have it that absent the bodily changes of old age, the changes from 50 to 500 might not be so extensive as one would otherwise expect. It's also probable that a being with a longer lifespan could take a proportionately longer time to reach emotional maturity. A 100- or even 1000-year-old immortal alien might be the equivalent of a human ten-year-old, while for immortal children who find Not Growing Up Sucks (or rocks) it may well be that having their clock stopped at a certain age also froze their cognitive development. They may get smarter, but not wiser.
Another part of this trope is that very often the apparent ages of immortals correspond to their status, so that the leaders are in their 30s with teenaged followers, even when their apparent age should have no relationship to their true age.
Might sometimes be a result of Crazy Sane.
If The Mind Is a Plaything of the Body, then this trope may result as a consequence. See Emotional Maturity Is Physical Maturity for the broader concept of physical age being more important than actual age as regards emotions.
- Some of the Soul Reapers from Bleach, particularly Rukia and Renji, alternate between acting like the teenagers they appear to be and the Really 700 Years Old warriors they actually are.
- Mina Tepes from Dance in the Vampire Bund seems to suffer from this intermittently. It is never made clear how much is an intentional put on, how much is her relaxing when not obliged to put up a strong front, and how much is neither; but there are times it is hard to remember that she is older than fifteen... and other times when it is hard to mistake her (despite her height and figure) for anything younger than fifty.
- Dragon Ball:
- God of Destruction Beerus is an immature Jerkass God who can be very childish, and acts like a Spoiled Brat. Always seeking out his favorite food, and prone to temper tantrums over petty reasons.
- Dragon Ball Super introduces the Omni-King or Zen-O, who is the ruler of all 12 universes and the Top God, able to one-shot the entire Multiverse if he wishes. Yet he behaves like a young child who is cheerful and easily excitable, and like a young child, he doesn't really get the full moral or ethical dilemmas of wiping out whole universes full of life.
- In Fullmetal Alchemist, Greed has a habit of referring to older humans in a disrespectful way ("old fart", "pops", and the like), which fits this persona/appearance as a punk in his early twenties. However, it's kind of odd when he's closer to three hundred years old.
- Tuka Luna Marceau is a 165 year old elf, but she looks and acts like a teenager. By the standards of her race, she was a teenager.
- Rory Mercury is 961 years old, but usually acts like a Fille Fatale 13 year old. However, she is perfectly capable of acting mature if she has to, like in an epic scene where she scolded a person who was disrespecting and criticizing soldiers.
- Every nation-tan in Hetalia: Axis Powers. Most of the characters have a "human age" of around early teens to late twenties, but being anthromorphizations of nations they are all hundreds or thousands of years old. They usually act more like their human ages (and sometimes even younger). Taken to the extreme with the bubbly and youthful China, listed with a Human age of 4000 and immortal.
- Inuyasha is about 250 years old (though he was in suspended animation for 50 of those years) and looks and acts like a petulant (and initially quite violent) teenager.
- The Wolkenritter from Lyrical Nanoha. Vita looks like a child, and acts like a child — though it could be fairly said that she's just immature, which is a problem that doesn't automatically go away with age. Her rather sucky role in life up to that point, and during the second season, probably also contributed to her lack of control via lots of emotional pain. Still, it's awfully coincidental that the most child-like Knight in appearance would be the most childish in behavior, given that they're all supposed to be the same age.
- In Mermaid's Scar, a subversion occurs when an immortal who has lived for 800 years as an 8 year-old boy only acts as a child to keep up appearances; his mind is anything but childish.
- Koumoto Akane from My Monster Secret is a devil and thousands of years old, yet looks and acts like a young teenager and a spoiled brat to the constant despair of her human great-great-granddaughter.
- Negima! Magister Negi Magi:
- Evangeline likes to act refined (difficult when she has to look up at the person), but sometimes lapses into childish whimpering (usually when she trips and falls). Whenever she starts to avert this and act her age, Chachamaru usually tells her "please don't start pretending you're old". She lampshades this on at least one occasion, laughing ruefully about how her pre-pubescent form influences her self-perception and personality.
- It's implied that Albireo "Colonel Sanders" Imma is much older than he appears. He spends a good chunk of his post-Tournament Arc appearance making fun of Evangeline. Especially her middle name.
- Yato from Noragami. Biologically in his early twenties, chronologically over 400 years old. It's not his primary characteristic, but Yato is often very playful and sneaky, often doing silly and childish things such as throwing a tantrum on the floor when Yukine says he doesn't want to go with him to Capypa Land. However, do not piss him off, as he can go from cute to terrifying in a heartbeat.
- In Pokémon: The Series, Mew is a Physical God and one of the oldest beings in existence, but still behaves like a young child.
- Lety from The Record of a Fallen Vampire is Really Fifty-Six Years Old but looks and acts like child (well, a child with incredible sniper skills). Her excuse: if she acted her real age it would appear "unnatural" and she'd have a harder time hiding among humans.
- Chibiusa, a.k.a. Sailor Chibi-Moon, from Sailor Moon looks and behaves like a five-year old. According to the manga, she's about 900. She still seems to find primary school to be challenging. Averted in the 90s anime, where she is around seven years old.
- The main devils of The World God Only Knows. Elsie is about 300 and behaves like a ditzy 12-year-old. Her classmate Haqua is a little better - but only a little, being about as emotionally mature as a human teen. It's a reliable source of humor in the scenes focusing on them.
- Somewhat back and forth in Fables. Most of the characters act like the thirty-somethings they are physically, except for Pinocchio, who, much to his annoyance, is still pre-pubescent. (Though for some reason the artist is fond of drawing him with a rather strong jaw.)
- One of the subplots in the latter part of Preacher is the general immaturity of the vampire Cassidy, and its destructive impact on not just himself but the people he comes into contact with.
- Topher, the vampire foe of the Runaways, is an aversion. He hasn't aged past being a teenager in 100 years. Hasn't stopped him from making a killing on the stock markets in the 1920s and losing it all in the Dot Com bubble.
- All of the Endless in The Sandman display this to a greater or lesser extent: Delirium is eternally childlike, and even dignified Dream has his moments of angsting like a lovelorn teenager. On the other hand, Death looks and talks like a teenage Perky Goth, but she is also one of the most mature and philosophical characters in the series and clearly knows the weight of her age and responsibility. Later issues imply that Death matured to become the quasi-teenage Perky Goth we all know and love: in her "youth," billions and billions of years ago, she was cold and cruel.
- In The Superhero Squad Show comic, Eternity is revealed to be an avid collector of entities.
- In Tom Strong, Tesla Strong, despite really being seventy-five years old, looks, acts, and is treated like a teenager.
- Wonder Woman Vol 2: Eros has never matured out of being a teenager in his main manifestation, and reflects the modern idea of a teen playboy. His brothers Phobos and Deimos are also pretty immature and often act like entitled teens. Amusingly their sister Harmonia is the opposite, being more mature than their parents Ares and Aphrodite.
- Selene Gallio, the Black Queen of the Hellfire Club in X-Men, is expressly identified as the oldest living mutant on Earth, beating even traditional X-Men Big Bad Apocalypse with a Time Abyss lifespan estimated to be somewhere in the neighborhood of 17,000 years. And yet, despite this truly vast pool of life experience to draw from, she is almost always mired in petty Decadent Court power-mongering, with only one serious attempt at becoming a goddess, and even that foiled because she's such an archetypal Vain Sorceress that just being called an "old hag" is enough to send her into a raging Villainous Breakdown. Indeed, her childish sense of self-image is so fragile that Danielle Moonstar of the New Mutants was able to make her have a panic attack, simply by using her Master of Illusion powers to generate the image of Selene as a withered old crone. She is also prone to flying into destructive rages when things don't go her way or she feels slighted, has a penchant for petty vengefulness and vindictiveness, and will go to great lengths to make people Brainwashed and Crazy just for fun before ditching them.
- In Incarnations Of Legends, the immortal goddess Amaterasu's fun-loving and tomboyish personality comes in stark contrast to the position she holds in real mythology as the highest god in Shinto mythology. She hates courtly etiquette and often speaks far more casually than she should, and she's so enraged when Haruhime's father disowns her that Amaterasu rolls up her sleeves and prepares to beat the crap out of him for it.
- Disscussed in the Steven Universe fic, I Want To Understand, when Vadalia refers to Amethyst as a kid, Greg points out that shes thousands of years old, to which Vadalia counters that shes still a kid in all practicality.
- In a The Lord of the Rings fic by A.A. Pessimal, Elrond glomily reflects on the problem with Elves being practically immortal is that those difficult teenage years - where your daughter sulks, throws tantrums, and brings home totally unsuitable boyfriends just to shock her parents - carry on for centuries.
- Mavis Dracula in Hotel Transylvania behaves like a typical teenage girl... despite being 118. Her dad has a few moments as well. It's justified in Mavis' case since she's been sheltered for much of her life and hasn't seen any of the world beyond her home, so she's not very mature as a result.
- Aisling from The Secret of Kells states herself in the opening narration that she's "lived through many ages", but she has the appearance of a little girl and often acts as childish as she looks.
- In Terry Jones' film Erik the Viking, the Norse gods are petulant children who don't care about mortals.
- Let the Right One In features Eli, a vampire who has been twelve for 'a very long time' but still acts pretty much exactly like a twelve year old. It is widely debated among fans, however, just how much her immaturity is the real Eli and how much is an act put on for the sake of getting a new Renfield.
- Mr. Magorium of Mr. Magorium's Wonder Emporium certainly counts. Of course, he does owns a magical toy store...
- Mortal Kombat: Annihilation's Big Bad Shao Kahn is a warlord so old he predates human civilization itself, yet all he wants out of life is to be the biggest Bad Boss he can be and to satisfy his father, the Elder God Shinnok.
- In Thor, Thor Odinson is several centuries old, but acts like a spoiled brat with a Hair-Trigger Temper. It takes being reduced to a mere mortal for him to finally mature.
- If anything, the movie The Old Guard is a subversion where centuries and millennia of experience have made the immortals more well adjusted, genuinely good people. Most notably, the homophobia that some bigoted soldiers show is called infantile by one of the immortals.
- Let Me In shows Abby. At first she seems to be inverting this trope because she is clearly more dominant in the relationship with her caretaker Thomas. But in the course of the plot it becomes clear that she is really stuck in the mindset of a 12 year old. She behaves innocently and childlike, likes to play with toys and puzzles, and is also completely ignorant of social norms. So she crawls naked into bed with Owen to cuddle with him and doesn't understand what he's upset about. Abby also kills a jogger, and just leaves the body lying there, which makes Thomas angry. The investigator who investigated the series of murders was able to find out very quickly where she lived. Finally she leaves town with Owen. It is unknown whether she turned Owen into a vampire or whether he will become her new caretaker. But as a caretaker, he would be a terrible choice because Owen is frail, shy, sensitive and skinny. So it's probably a childish crush that leads Abby to take Owen with her.
- The Kurgan in Highlander was a violent wild barbarian when he first became an Immortal. Over a thousand years later, he's still a violent wild barbarian.
- Firo tries to avert this in later volumes of Baccano!, as getting mistaken for a fifteen-year-old is just as annoying at ninety as it is at nineteen. He is spectacularly bad at it, however - he still talks to his wife of twenty years like a boy asking out his first crush.
- High Elf Archer from Goblin Slayer is 2000 years old and is far older than the rest of her party, but her behaviour (sheltered, easily provoked, and uncouth) makes her the least mature of them all.
- Chizuru of Kanokon. On the one hand, she is a fox spirit, with all the instincts that entails, but on the other, she's four hundred years old, so you'd think she'd know that trying to rape a young boy is bad manners. Her mom is a little better but still has entirely too much fun with said shota herself.
- Tet from No Game No Life looks and behaves like a child, despite being the Physical God of Games.
- Holo from Spice and Wolf looks and usually acts like a girl in her teens despite being a harvest god hundreds of years old.
- The Twelve Kingdoms: There are immortal characters who are over a hundred years old, but still act and consider themselves as teenagers. Immortality here stops not only someone's physical maturation, but also their mental and emotional maturation. An immortal who looks 12 years old effectively still is 12 years old regardless of how old and experienced they actually are.
- In The Chronicles of Amber, most of the Amberite Princes initially think and act like charmless Royal Brats, but as the series goes on and conflicts force them to work together, develop into The Wise Prince.
- Lampshaded with the "teenaged" vampires in Carpe Jugulum, who are three hundred years old, and wish their parents would treat them as such... but don't act it.
- Also, Granny Weatherwax to the Queen of Elves in Lords and Ladies:
"You call yourself some kind of goddess and you know nothing, madam, nothing. What don't die can't live. What don't live can't change. What don't change can't learn. The smallest creature that dies in the grass knows more than you. You're right. I'm older. You've lived longer than me but I'm older'n you. And better than you. And, madam, that ain't hard."
- Discworld's gods tend to be rather lacking in maturity as well as brains (thinking is what worshipers are for). It always irritates Discworlders with pretensions to culture that the gods are very lower-middle-class in their tastes regarding art (they would consider three plaster ducks as avant-garde) and music (a musical doorbell counts as an uplifting artistic experience). Even their home, Dunmanifestin, is basically a retirement community rife with noise complaints and refusing to return a neighbor's lawnmower.
- Small gods, who haven't attracted any followers, are even moreso: a pinch of ego and some willpower.
- The original Dracula, a vampire hundreds of years old, is a bit complicated in this respect. As explained by Professor Van Helsing: "Well, in him the brain powers survived the physical death. Though it would seem that memory was not all complete. In some faculties of mind he has been, and is, only a child. But he is growing, and some things that were childish at the first are now of man's stature. He is experimenting, and doing it well."
- In Dragonlance, Paladine, the god of good, when in his avatar form is rather a comic figure. Some of that might be Obfuscating Stupidity but it is implied that some of it is also his real character.
- The Dresden Files has the Winter Lady Maeve. She is at least hundreds of years old. She has a body that can attract most anyone she wants. She is also one to throw temper tantrums when things don't go her way. In Cold Days it is implied this is not just because of Maeve's age but the Mantle of the Winter Lady which she gave into years ago. Should another woman take it from her and give into the power, in ten to twenty years she wouldn't be that different from Maeve.
- The gods of David Eddings' The Elenium are prone to some rather immature emotionalism. It's explicitly explained by the world-weary Sparhawk as almost stemming from their immortal nature; having never needing to fear death or be chastised they don't develop maturity as well in some aspects of their personality. Curiously, the least immature Styric deity in Sparhawk's world seems to be Aphrael, the Child Goddess. One of her brothers, Setras, appears more concerned with sunrise artwork than with humans and has to have every plan explained to him in words of one bit that words are made out of.
- Lampshaded in Everworld while most of the gods that the protagonists had met up until that point were psychopaths, seeing a whole pantheon together on Olympus really helped them see how lazy, self-obsessed and petty they could be. April actually figures out that gods cannot change their personalities are basically set based on their role, so that getting them to act contrary to that position is nearly impossible. Athena, the Only Sane Man among the gods, confirms this.
- In "The Gypsies in the Wood", Charles Beauregard investigates a series of incidents in which The Fair Folk steal and impersonate children. At the end, he reflects that in his experience the Fair Folk are themselves much like children in some ways, selfish and given to extremes of emotion, "prone to spasms of joy and long rainy afternoon sulks", aptly called the little people.
- In The Hitchhiker's Guide to the Galaxy, Wowbagger the Infinitely Prolonged has made it his mission to insult every being in the universe, personally, in alphabetical order. Which only began after the awesomeness of being immortal finally wore off and the eternal boredom set in.
- Honor Harrington occasionally addresses the implications of slowing the aging process and how much of your personality is influenced by hormone levels based on your age. Puberty and its associated mood swings has years added on to it.
- In Julie Kagawa's The Iron Daughter, Meghan observes that the Unseelie Court acts like the teenagers at her school.
- Virtually every immortal from the Iron Druid Chronicles are narrow-minded, short-sighted, vindictive jerks prone to throwing tantrums or taking petty revenge for an slight real or imaginary. Its kind of expected from the gods given how they are portrayed in the series. Yet, mortals who became immortal are almost always the same including the main character. There are a few exceptions, such as Jesus.
- In The Legends of Ethshar novels, eternal youth spells freeze someone at that point in their maturity, and immortal wizards who revert themselves back to youth note that a younger body makes them act differently (especially as regards the libido.) One immortal who's been 15 for 200 years is eventually dumped by her 16-year-old beau as being too young (emotionally speaking) for him.
- It's specifically noted that her emotional immaturity results from her miscasting the eternal youth spell: essentially, she's cursed to never grow up. Other eternally young wizards behave more like an old person in a young body.
- Avoided at first with Eli, a vampire who's been twelve for a long time in Let the Right One In. She doesn't act or think like a child, but begins to (possibly subconsciously) do so when she starts hanging around with the main character.
- Notably averted in the case of The Lord Ruler of Mistborn: The Original Trilogy. His extreme mastery of allomacy and feruchemy gives him functional immortality as a strong, healthy, youthful man. Almost every encounter with him, however, goes to great lengths to stress how ancient, tired, and apathetic he comes off as despite his outward vigor.
- Lampshaded in Ken MacLeod's novel Newton's Wake: A rejuvenated woman says people like her just get a bit "cannier", and passes the rest of it off as fatigue poisons and neural decay.
- Sam and Hailey from Only Revolutions, who are "allways [sic] sixteen".
- Peter Pan is all about this, his skills with a blade on par with those of Captain Hook notwithstanding. Justified in his case, since his overwhelming desire to be immature is why he became immortal in the first place.
- In The Picture of Dorian Gray Dorian's painting ages for him and takes the cosmetic consequences of his sins, which allows him to commit hideous crimes without consequences to him.
- The gods of Dweia from Eddings' The Redemption of Althalus are also prone to immature emotionalism, though to a lesser extent, and with the same reason given.
- In The Secrets of the Immortal Nicholas Flamel, Billy the Kid, who was still a young man when he was given immortality, and, well, lives up to his nickame. His main immature traits are constantly referencing movies and TV and being a reckless driver.
- In Harry Turtledove's Tales of the Fox series, the gods are Spoiled Brats because, being nearly all-powerful, no one can discipline them. The only exception is the All-Seeing Ikos, and even he can be manipulated by his pride.
- Edward and his siblings from Twilight. With the exception of some very adult takes on death and sex, they all act like the teenagers they look like. It's explained in the books that this is a result of becoming a vampire; the ex-human is frozen in time both physically and mentally. Doesn't explain why Bella thinks that Edward is oh-so-mature though.
- A more frightening take on this is the immortal children: a child who becomes a vampire will never be able to gain the self-control of an adult vampire, and will instinctively slaughter everything instead. Combine that with super-vampire strength, speed, etc. and the supernatural ability to make anyone who lays eyes on them fall obsessively in love and fight to the death to protect them, and it's no wonder it's illegal to bite children.
- The White Queen in The Unexplored Summon://Blood-Sign. Her actual age is unknown, but she looks like a teenager, and acts like a small child. This includes having no empathy for anything except the sole thing she's interested in. She has no problems with destroying the world if it gets her what she wants.
- The fey in Wicked Lovely. They are immortal, or at least Really 700 Years Old, but they very rarely act or look anything more than early-twenties. Probably the best example is Keenan, who is a 900 hundred year old teenager in pretty much all respects.
- Invoked in N. K. Jemisin's Inheritance Trilogy by Sieh, the god of childhood and mischief. Even though he's the unutterably ancient first creation of the Three Old Gods, he chooses to embody his affinity fully, and almost always acts like a ten-year-old (albeit an all-powerful Tyke Bomb one). Indeed, acting like an adult or undermining the concept of childhood sickens and weakens him.
- The Shadowhunter Chronicles shows Magnus Bane. He often shows rather immature behavior. It later turns out that this is not uncommon for warlocks. They are immortal, and when nothing can surprise them, they petrify inside.
- Jem Carstairs is not exactly immature, but for someone his age, he still seems quite young mentally. It is later revealed that he is also good at dealing with teenagers when he takes Kit Herondale into his home. Before that, he'd enjoyed being around other teenagers like Clary and Simon.
- Lily Chen is a vampire and is almost 130 years old. Nevertheless, she always tends to joke and other humorous things.
- An episode of Being Human features Adam, who was turned into a vampire as a teenager and fed blood by his parents until they died when he's technically in his mid-40s. He behaves VERY much like a bratty teenager, largely because his parents kept treating him like a child his whole life. When he's forced to grow up a bit after their deaths, he does manage to mature pretty quickly.
- Older vampires on Buffy the Vampire Slayer and Angel tend to project "moderately clever adult who's been around the block a few times" more than "old man". Angel's interest in looking cool is occasionally lampshaded as age-inappropriate, despite the series stressing his maturity relative to the teens and 20-somethings he hangs out with. This exchange between Buffy and Angel stands out:
Angel: You know, I started it. The whole "having a soul". Before it was all the cool new thing.
Buffy: Oh, my God, are you twelve?
- Anya was also something of an interesting case. Her behavior was explainable at first due to her life as a demon that had no relationship with humans. When it was eventually revealed that she was a human at one point in time, however, the explanation was retconned simply by demonstrating that she was always just plain weird. Spending eleven hundred years as a demon also contributed.
- Spike, a vampire over a hundred and forty years old, mopes like a teenager when Drusilla breaks up with him. He gets some motherly advice from Joyce Summers, a human woman a fraction of his age. (The fraction in this case being 'less than a third but more than a quarter'.) Unlike his polar opposite, Angel, his flashbacks to the past usually involve a bonfire, mod clothing, or a disco.
Angel: Wait a minute.... I wasn't in Italy in the fifties!
Spike: Oh, right. Guess you weren't. (beat) Really missed out.
- Put Angel and Spike in the same room, and they start going at it like a pair of teenagers. Wesley, a human man much younger than either of them, once expressed shock that they could spend 40 minutes intensely arguing about whether or not cavemen could defeat astronauts in a fight.
- Buffy's original college roommate, Kathy. She acts like a typical college freshman, but it turns out she's a demon and thousands of years old. (She's also in big trouble from her guardian.)
Kathy: [whines] I'm 3000 years old! When are you going to stop treating me like I'm 900?!
- Mason and Daisy on Dead Like Me both died in their twenties decades ago. Daisy is still insecure and moody most of the time, and Mason is still seriously immature even for someone in his twenties. Roxy, who hasn't been dead as long, acts significantly more mature, and George, who died as a teenager and is still roughly a teenager by the end of the series, does enough growing up that she often seems to be above Mason and Daisy's juvenile behavior.
- Doctor Who:
- The Doctor, who stole a (admittedly outdated) hyper-advanced time machine and left the most advanced civilization in the universe so that they could go sightseeing, and in general shuns any sort of responsibility. Special mention goes to Four, who provides the page quote and ran around munching on candy, and Eleven, who is obsessed with looking cool and gleefully proclaims that he's a madman with a box. Even One got in on the act, starting out acting like a spoiled teenager. And despite being one of the more mature-looking of the Doctors, the Twelfth Doctor eventually took on the persona of an aging rocker.
- The Master is frequently portrayed as a Psychopathic Manchild, especially the Anthony Ainley and John Simm incarnations, to help cement them as the Doctor's Evil Counterpart. In the 2007 series, the Master successfully takes over the world, and alternates between burning down whole countries and blasting the Scissor Sisters while mocking his captives.
- In Hercules: The Legendary Journeys and Xena: Warrior Princess, the gods are pretty much just 30-year-olds (or even 12-year-olds that look 30) with big egos. Surprisingly accurate to the original mythologies, in which most of the pantheons were Jerkass Gods.
- Subverted in Highlander. While some Immortals act childish at times and some of them look quite young, they would not survive for long if they weren't willing to kill or be killed.
- One Immortal kid uses other peoples' expectation that he is innocent and nonthreatening to get them to lower their guard.
- The teenage vampire on Moonlight in the episode "Arrested Development". He was 200 years old and acted like an angsty teenager. It was blamed on permanent hormones, but the writers seem to have forgotten that 200 years ago, someone his age could get married and would be treated as, and act as, an adult member of society.
- Trelane, in the Star Trek: The Original Series "The Squire of Gothos", is an extremely powerful near-god and hundreds if not thousands of years old, but acted like a child...and by the standards of his race, he was—his parents showed up at the end to drag their whining kid home.
- The children in the TOS episode "Miri" are Really 700 Years Old but still act like children.
- Q from the Star Trek: The Next Generation started off this way: looks to be 30, huge ego, power to match. He intentionally introduced the Federation to the Borg and put "Humanity on trial" just to make things interesting and test to see that Humanity had what it takes to be allowed to even exist. This childish behavior went on for a few seasons before the other members of the Q continuum punished him for the above mentioned reasons by taking away his powers and temporarily leaving him as a mortal. This lead to some Character Development in Star Trek: Voyager. He still liked to show up unexpectedly and sometimes pull off the occasional harmless prank, but there were bigger problems going on in the Q continuum that forces him to be more mature. (A popular fan theory is that Q is Trelane's older brother.)
- Jadzia Dax, though not technically immortal, has several lifetimes of experience. Yet you wouldn't know it if they hadn't told you about it. It doesn't help that the Dax symbiont's host from before Jadzia was a Dirty Old Man, and that the lifetime of experiences of previous hosts directly affects the personality of its current host, with the previous host being the most influential.
- Few of the vampires in True Blood show signs of having lived for centuries and through previous ages of history. Many of them are surprisingly immature. This is particularly played for laughs with the Queen of Louisiana, who spends most of her time forcing her minions to play children's board games with her. Bill, one of the younger vampires, is one of the few who actually displays antiquated speech and mannerisms.
- Rebekah from The Vampire Diaries is a 1000-year-old vampire who's interested in cheerleading, boys, and the prom. Curiously, her brothers (except for Kol) actually do act their age, leading to some fans to ponder whether a double standard is at work.
- Damon Salvatore qualifies as well being impulsive, decadent and obsessed with Elena.
- The ancient Greek gods are constantly interested in the affairs of mortals; they also breed with mortals. They don't seem to learn anything from experience, as far as wisdom is concerned. They are petty, cruel and constantly fighting amongst each other.
- Destroy the Godmodder has many of these, least of all being the godmodder himself.
- In Ars Magica, the rare few mages who transform themselves into truly ageless beings find that their "essential nature" becomes fixed and unchanging, which makes it immensely hard for them to develop as individuals. The best they can do is imbue new knowledge into a magical talisman, but they regress to the mental state they had when they gained immortality if they lose access to the talisman.
- For changelings in Changeling: The Dreaming this trope is essential if they want to keep their Fae side intact. Though changelings tend to age much more slowly than other humans, eventually Banality will weigh heavily on their Fae souls and they become Undone. They constantly struggle to resist the pressures of growing up to hold on to their magic and immortality for as long as they can. Changelings are basically humans who have been given an Immortal Fae soul that may have been a powerful being in of itself and is merely body-hopping to survive. The humans they inhabit tend to be quite young. So it is possible, and quite common, to have a millennium old legendary dragon-slayer, a highly respected duke of the Seelie Court, or a highly valued scholar of ancient lore sitting in a living room playing with toy trains until mommy calls him for bedtime.
- The 3.5 edition D&D supplement Libris Mortis has this as one of the cons of becoming a lich. While a lich has an eternity to learn, they can't change. They'll always have the same mindset and beliefs they did when they transformed.
- The 200-year plus necromancer Liliana Vess from Magic: The Gathering is fully revealed to be this once she joins the Gatewatch: highlights include pranking Jace by rearranging his books, refusing to refer to Gideon as anything other than variations of the term "beefcake" and goading the already immature and impulsive (due to actual youth) Chandra into getting into trouble, to the point that even she calls her out on this:
Chandra: Liliana, you're two centuries older than me. Exactly which of us is supposed to be the responsible one?
Liliana: Let me tell you a secret. There doesn't have to be a responsible one.
- Subverted in the Ravenloft supplement Van Richten's Guide To Vampires, which proposes that vampires go through a psychological maturation-process which commences when they become undead, and is entirely independent of their mortal age. An octogenarian who becomes a vampire can regress to teenage-brat behavior, while a child-vampire who's (un)lived long enough can become a sober, calculating Chessmaster.
- Vampires in White Wolf's Vampire: The Requiem and Vampire: The Masquerade canonically tend to be "frozen" at where they were when they first became Vampires. They do become more knowledgeable and powerful, but they often keep the same prejudices and emotional maturity they had from when they were still alive. Therefore, even though a vampire may be 200 years old, he could still act like a hot-tempered 17 year old. Functionally, this trope pops up a lot due to the simple fact that a bunch of mortal players are dictating the characters' every action on the fly.
- Most versions of Bumblebee are treated like an inexperienced child, despite being older than humankind. In fairness, some versions (especially his Transformers Animated iteration) do act like a child.
- Hot Rod (or Rodimus, or Hot Shot) is an even bigger offender in this regard, but it's worse since he's frequently Optimus Prime's successor.
- The angels and demons in the Disgaea series are all over a thousand years old, but since time flows differently in their dimensions, they age 100 times slower then normal and act exactly as old as they look.
- Drakengard is an unusual example in that the immortal started out immature- Seere is a six-year-old who gave up his time to be in a pact with a golem, meaning he'll be a six-year-old forever.
- Xiaomu of Endless Frontier and Namco × Capcom. She may be a 700+ year old sage fox, but she can be immature about certain things, enough to be even spanked for them.
- Final Fantasy:
- Red XIII from Final Fantasy VII is 48, but, with his species living for centuries, has the maturity level of a human in their mid-teens. Initially he talks in a fancy, intellectualising way, but this is eventually revealed to be an extremely teenage affectation, and he switches to more childish language and presentation afterwards.
- Prishe from Final Fantasy XI is a Hot-Blooded Tsundere. Granted, she's only in her 30s chronologically, but she doesn't act 30.
- Fire Emblem:
- In the Fire Emblem Archanea games: Tiki, a 740 Manakete(basically a Were Dragon) looks and acts like a little girl, in contrast to the other manaketes who act maturely. This is eventually justified as its revealed all but 10 of Tiki's years of life was spent in a forced sleep and in the ten years she had awake, she spent with her stepfather Bantu raising her as a normal girl. Also Xane is revealed to be a Manakete as well and looks like a teenager, yet he usually acts like a childish clown. This is eventually revealed to be partly an act as Xane is eventually revealed to be sad and cynical on the side after having seen the fall of dragon kind.
- Fire Emblem Awakening:
- In Fire Emblem Awakening (a loose sequel to Shadow Dragon), Tiki is the much revered and millennia old Voice of the Divine Dragon, who normally acts wise and aloof, but her profile explicitely mentions that she also has a more childish side. Say'ri experiences this firsthand when Tiki first Blows A Raspberry at her and then tries to stuff her mouth with an apple in their B support.
- From the same game, Nowi is another Manakete and a young Tiki Expy, just like her she is more than hundreds years old, but has the looks and mindset of a young girl. English only material says that this is at least partly a case of Obfuscating Stupidity. Japanese material and english DLC says its Proportional Aging.
- Harvest Moon:
- The Harvest Goddess introduced in Harvest Moon: Back to Nature is an immortal goddess who acts like a spoiled teenager. Even if you marry her, she's barely present in you or your child's life.
- The Witch Princess from Harvest Moon DS is the Harvest Goddess' rival and is just as bratty as her.
- The Harvest Goddess in Harvest Moon: Light of Hope acts like a bubbly Genki Girl despite being hundreds of years old. She also has a strong Sweet Tooth for strawberry jam because a past mortal lover always gave her strawberry jam.
- Viridi from Kid Icarus: Uprising. She's the Goddess of Nature, and thus probably as old as the Earth itself, but she has the appearance and personality of a bratty eight-year-old girl.
- Zoe of League of Legends. Granted immortality by the powers of Targon at 12, she still appears (And acts) like the same immature kid she was the day she became an Aspect.
- Mother 3 has Porky. He will stay that way forever due to both time warping too many times and for trapping himself in the Absolutely Safe Capsule at the end of the game.
- All of the four goddesses of Neptunia exhibit this trope, one way or another.
- Shadow from Sonic the Hedgehog is over 50 years old, but is physically the same age as Sonic, who is only 15. As a result, Shadow acts like an angsty teen and has his childish moments, especially in the Archie comics.
Rouge: And we all almost died because you two [Shadow and Knuckles] got distracted beating each other up. But that's behind you now since there's bigger issues on hand—Right?
Shadow: ...he called me a jerk.
- Many Touhou Project characters, though it might be side-effect of how most characters are immature and most are Really 700 Years Old, with predictably frequent overlap.
Tenshi: Every day is singing, singing, drinking, dancing, and singing again, over and over... I was bored out of my mind! So I came down to the surface and watched you playing with all kinds of different youkai... Seeing that made me think, "I want to play disaster resolution too." So I caused one. A disaster, I mean.
- The Scarlet sisters are the most obvious example, as they gained immortality by forgoing maturity, with Word of God stating that "creatures of [Remilia's] kind forfeit their growth and maturity in exchange for eternal life. In other words, she can live forever because she never grows up." Thus, they have the appearance and mentality of ten-year-old children. Remilia at least has the experience to act mature and can get serious if required, but Flandre doesn't even have that, what with spending 500 years in their mansion's basement.
- Kaguya Houraisan kept up a centuries-long war with Mokou where they killed each other daily (for Mokou it was one part revenge, two parts something to pass the time), and treats her servants like playthings for her amusement. How Eirin (an actually mature immortal) puts up with her is anyone's guess.
- Yukari Yakumo is at least as old as Gensoukyou but spends most of her time sleeping, and when she's awake she messes with people and gets her shikigami to do the heavy work for her.
- All fairies are excellent examples of this trope, which is justified due to The Fog of Ages and usually being on the younger end of the immortal scale. Cirno is probably the most notable among them and one of the biggest ditzes in the franchise, followed by Clownpiece, who is implied to have lived since at least the times of ancient Greece, but is willing to set the house of her landlord on fire for fun. The Three Mischievous Fairies are a less certain case as it isn't made clear on whether or not they're actually older than humans age-wise.
- Subverted with Suwako Moriya. Despite having the appearance and mannerisms of a little girl, there are a lot of indications that her childish behaviour is largely an act and that she's a good deal more intelligent than she lets on. She is, after all, a goddess who has existed since ancient times.
- This is Tenshi Hinanawi's problem. Most Celestials achieve their status through diligence and careful introspection in their lives, as well as the ability to fight back against Shinigami; her clan was quickly whisked up to the heavens by a kami for good work maintaining geologic keystones.
Tenshi: I don't want to go on living the boring life of a celestial forever.
- Joshua from The World Ends with You. Fantastic godlike powers, but he spends his days loitering around Shibuya trolling Neku. It's assumed that he was a troll in life, and immortality hasn't caused him to grow out of it, despite his job's responsibilities. Hanekoma might count as well, though his age is never given.
- Xenogears features several characters who are quasi-immortal. Some have lived for hundreds of years, a few for as many as ten thousand. Emperor Cain and the Gazel Ministry act as one might imagine. The former is a world-weary, very old man who has kept his moral compass intact due to guilt over a sin committed long ago, the latter being very anxious to transcend to a higher level of existence and possessing of no moral compass whatsoever. Then, there is Miang, who has lived as long, but in a different manner: she possesses a new body when her current one dies. When we meet her, she has the body of a beautiful young woman and appears to act like one, being flirtatious and sexually-active. Yet, it's difficult to tell how genuine this is, because her entire existence is devoted to executing the mother of all plans, and everything she does serves this end.
- Arcueid Brunestud from Tsukihime is also much like the previous entries. She's an ancient True Ancestor, but she was bred to be a weapon and not a person by her own race, and so they kept her asleep all the time except when she was sent to kill someone... so her demeanour on the outside world is not unlike that of a curious and confident child, marveling at everything new she comes across and being generally naive and emotionally outspoken. She really isn't any older emotionally than she acts.
- When They Cry:
- Higurashi: When They Cry:
- Rika, despite being Really 700 Years Old, her outward behavior and speech patterns are still those of an adorable, cheerful girl. As it turns out though, this is only an act so as not to alarm everyone who's oblivious to Hinamizawa's dark secret. Mentally, she's a rather serious adult. That said, she hasn't grown nearly as old mentally as she thinks she has.
- Hanyuu, a.k.a Oyashiro-sama, who's even older, but is really quite shy and easily flustered. As it turns out, this is also much of an act (though not all of it). For one, Hanyuu died as an adult. There are multiple times where she drops the act and seems as mature as expected from her (which is jarring because her current form is that of a Cute Ghost Girl). The anime adaptation exaggerated her immmaturity while dialing down her maturity.
- This trope is played with in several ways with the witches from Umineko: When They Cry:
- Beatrice is perfectly capable of being the dignified and elegant witch that she claims to be, but is often very childish and mischievious. This is because she's not actually a thousand years old like she claims. She's actually 19 years old.
- Lambdadelta is supposedly a great witch herself, but usually comes across as something of a ditz who's obsessed with fellow witch Bernkastel. Another subversion, since her childish behaviour is really just an act.
- Bernkastel appears to avert this, being rather cold and emotionless, though this is also subverted since she's not as emotionless as she seems, and as her displeasure at losing shows more as time goes on, she actually seems to show more immaturity.
- Higurashi: When They Cry:
- Mab and most of the other Fae from Dan and Mab's Furry Adventures, sort of. Essentially everything they do is a matter of "It Amused Me," but they operate and think in an entirely different way from anyone else, and evidence suggests that they can also be mature if that's what amuses them at the time. Additionally, since they're immortal and have a flexible view of time, this behavior might be a way to avoid going totally insane. There is also a somewhat sinister slant to their apparent immaturity, especially given their general view of things as being a game of sorts, and that fact that despite near-omnipotence they will still allow their friends to die in preventable ways.
- This behavior also appears in some of the mortal-but-extremely-long-lived characters. Abel and Kria don't always act like they are in their 400's. Dan and Regina have some excuse though since they actually are in their 20's.
- Incubi and succubi in general are creatures of emotion, and apparently have a harder time controlling their own in turn, though the clan leaders are more than capable of being serious - perhaps because they are millennia old. Demons have no such excuses, however.
- This behavior also appears in some of the mortal-but-extremely-long-lived characters. Abel and Kria don't always act like they are in their 400's. Dan and Regina have some excuse though since they actually are in their 20's.
- Misa from Errant Story is about 1,500 years old yet frequently acts like she's 15. She has been doted on her entire life though.
Misa: "Being the youngest of a race that lives forever means being eternally treated as the baby."
- El Goonish Shive takes the effort to make it a Justified Trope as the immortals erase their own memories to avoid the complete boredom involved in knowing everything.
- From Homestuck:
- Even though some of the pre-scratch ancestors have existed for so long time has lost all meaning for them, they all still act just like awkward, silly, hormonal teenagers. This may be because they're dead and thus removed from the mechanisms that cause change in life. Sanity Slippage, or at least Took a Level in Jerkass, is also implied for most.
- Her Imperious Condescension is a galactic conqueror who is over a thousand years old, yet the few times she speaks, she uses either ghetto speak or pink sparkly text.
- Lord English himself qualifies. While his actual age is really hard to quantify, he has certainly been around for a very long time. However, due to certain actions he took in his youth, his emotional development was stunted pre-adolescence. According to the author, he's the same psychopathic little tool he was in his youth, just much stronger now, and he will never, ever grow out of it. He hasn't even matured physically either — his "adult" appearance is implied to be the result of his soul merging with others, including the muscular Arquiusprite. Hinted at by the fact that true adult Cherubs have wings while Lord English does not.
- Pete the Gryphon and the Spirit Dragon in Housepets!. While the portrayal of their Cosmic Chess Game as a tabletop RPG is just a metaphor King can understand, the fact they're constantly rules-lawyering, accusing each other of cheating, whining to the game-master, and generally bickering like teenage siblings seems to be depressingly literal. When they get reincarnated as a pair of mortal fox kits they actually come across as more mature.
- The undead warlock Richard from Looking for Group borders on Manchild at times.
- The angels Rumisiel, Cassiel, and Vashiel from Misfile range from 437 years old to possibly several thousand years old and yet still act like teenagers. Vashiel is somewhat more believable, just deeply honest (to the level that it's physically impossible for him to lie) and highly clueless about stuff he hasn't paid much attention to in his long history of smiting.
- Nebula: It's especially prominent with Earth and Uranus, but none of the main characters display the maturity you'd expect from eons-old Anthropomorphic Personifications.
- The Order of the Stick:
- Xykon is not particularly mature for an immortal lich with more than a century of life behind him. Start Of Darkness reveals that he was never very mature to begin with, even as an eighty-year old man. He even lampshades how, even at his advanced age, his "life's wisdom" boils down to little more than "sure, being a badass villain is a barrel of laughs, but what's the point if you can't even enjoy the little things in life" (which to him is mostly watching people die gruesomely and drinking coffeenote ). That said, Xykon can be surprisingly clever and patient if he wants to.
- Redcloak is another example, played in a different way. His aging processes have been retarded by the magical cloak he wears, and he's eventually called out on this by his (normally aging) younger brother: He's spent most of his time following the Dark One's directives (and later, Xykon's) and hasn't used any of that time to actually live a life; and because he never ages, he hasn't been forced to move on from the tragedy of their past the way Right-Eye had to.
- Both used and subverted in Sluggy Freelance. The magician Kesandru has grown more mature over the centuries. However, he also still seems to think that pulling a rabbit out of his hat should be enough to frighten people into submission.
- In Templars of the Shifting Verse Augustus, Loria and Dantes all became immortal at an early age — so they have limited real life development outside of their adventures.
- Plenty of Regulars and Rankers in Tower of God are pretty immature in spite of being hundreds to thousands of years old.
- Ranker Quant Blitz is so impulsive he gambles away his whole fortune in one go in a suspicious game centre in the middle of nowhere.
- Princess Endorsi Jahad reportedly didn't even start climbing the Tower (ie. become a Regular) until she was around 300 years old, but she acts like a mildly sociopathic, hyperacive teenager, refusing to take responsibility, freaking out whenever someone accidentally implies she's not the prettiest girl around, and kicking people in the head when she's displeased. The older princess and High Ranker Yuri Jahad is like a more mature version of her, but that's only relatively more mature. Yuri once manages to convince her own weapons she's an idiot.
- Though it's probably not supposed to apply to everyone who's an example here, like Yuri, Evan Edroch once vaguely explains a form of this trope: "Sometimes Rankers live so long that they end up becoming more like little kids." He's specifically bringing this up to explain why Yeon Woon would have been so naïve as to give away most of his power to a bullied underdog, who used it to kill a lot of people who had wronged him and then refused to give it back.
- Justified in 17776: After 15 000 years of Complete Immortality, humanity has settled into a comfortable Anti-Nihilist rut, spending their time on hobbies like ever-more-absurd variants of football. The newly self-aware AI Nine finds it uncanny, but Ten explains that past a point, comfort and familiarity took precedent over ceaseless striving.
Ten: Struggle — true, unfabricated struggle — is a cocoon they have shed. Humans are beings of the land and sea who have refused to cast themselves into the cosmic zoo. Exploration and conquest are meaningless. They have achieved their final form, and they are resting in an eternal moment. They are creatures of play. They will be creatures of play until the end of time.
- Many of the main cast of If the Emperor Had a Text-to-Speech Device are over ten thousand years old, and very few are above petty and childish antics. The Emperor Himself alters the Astronomicon (a giant space beacon that all Imperial ships use to navigate the Warp) into the shape of a giant middle finger, Magnus the Red giddily rides a warbike like a child given his first bicycle, and even Rogal Dorn requests a bedtime story from the Emperor (albeit a dry series of textbooks called Ten Books About Architecture).
- Adventure Time has both Marceline and the Ice King, who despite being just over a thousand years old, both haven't progressed past the maturity of the average teenager.
- In Marceline's case, her perpetual It Amused Me attitude towards life comes from two things. First, all the crap that's been dumped on her for a millennium, with the earliest incidents being the death of her mother and seeing her Parental Substitute Simon slowly become the Ice King, leading to a personal rule of emotional detachment. Second, she became a vampire as a teenager, running into that frozen cognitive development issue mentioned at the top of the page; this is actually the driving force for an entire mini-series where Marceline becomes annoyed by her own arrested development and seeks to solve the issue.
- The Ice King's behavior is wholly the result of his magic crown slowly destroying his mind the more he used it, transforming him from a mature and loving father figure to a Cloudcuckoolander with no memories of that past life.
- Takua, one of the oldest beings in BIONICLE at 100,000 years of age, likes to put glowing plants on his head and run around pretending to be a bunny rabbit to relieve stress. He gets leeway due to his periodical bouts with amnesia. Gresh, older than a hundred millennia is also regarded by those around him as an inexperienced kid, especially since his strong sense of honor and justice makes him come off as rather naive in his Crapsack World.
- In Foster's Home for Imaginary Friends, the Imaginary Friends don't age, either mentally or physically. Since they were made to be childhood companions, they're almost all intrinsically child-like. Ones who act more mature, like Wilt and especially Herriman, just happen to have been born that way instead.
- Futurama: Parodied in the episode "Where No Fan Has Gone Before": When the Energy Being Melllvar's mother drags him off to dinner, Fry makes a Star-Trekky comment about how they thought he was a mighty, god-like being, but he was only a child (see Trelane, above). Then his mother says, "Child? He's thirty-four," playing up the Basement-Dweller trope.
- Demona is this all the way. Macbeth doesn't suffer from the same problem, despite having received their immortality in the same way, likely because even when Demona was an old woman she was still an immature punk, while Macbeth was fairly mature as a young man.
- The Children of Oberon frequently act like children. As Greg Weisman said, they have "Great power. Little or no responsibility," and with Complete Immortality never both worrying about disease or even starvation. They get to spend their whole lives playing games and fighting each other. They aren't necessarily evil, but even the best of them don't seem to grasp morality.
- Ironically, the series implies many of them were once worse. Oberon leveled a 1,001 year exile to force them to grow up. It worked on a few of them. (Extra ironically: some are actually more mature than Oberon himself now.)
- Bill Cipher of Gravity Falls has lived for trillions of years, but half the time acts like this creepy clown or sadistic comedian. The way he describes his plan to invade our dimension sounds more like a guy who's planning to hit the town with his buds than universal domination. According to the show's creator, "Bill is a character who's been around for countless billions of eons, but he hasn't grown up in that time." This helps highlight the show's Coming-of-Age Story, especially as the last few episodes juggle Bill's invasion with the twins trying to define themselves as they reach teenage-hood.
- Justice League's version of Wonder Woman often acts like a young girl (especially when dealing with her mother, Hippolyta), despite physically being a twentysomething woman and actually being several thousand years old. Possibly justified since she spent most of her life on Themyscira under her mother's rule, cut off from the outside world.
- Mordred, the son of Morgan La Fay, has a severe case of this. His mother used her magic to stop his physical growth so he doesn't age until he's ready to be a king, but in doing so evidently also stunted his emotional growth, since he still acts like a ten-year-old Royal Brat. This is exploited by the heroes, who trick him into using his magical power to turn himself into an adult, which works a little too well for him.
- My Little Pony: Friendship Is Magic:
- Discord is far older than even the millennia-old Princess Celestia, but as the spirit of chaos is only concerned with spreading his concept of fun and excitement. He's also an omnipotent Reality Warper with a passion for psychological torture. Not a good combination. He finally grows up a bit after 1) forming a friendship with Fluttershy and 2) getting a taste of his own medicine after Tirek betrays him.
- Princess Luna, despite being able to measure her age in millennia like her sister, is a lot less mature. Even after she is freed from being Nightmare Moon, she still has a Hair-Trigger Temper, is prone to mood swings, and seems to get along better with children than adults. On the other hoof, she takes to her responsibilities with pride and dedication.
- The Mask:
- Skillit is 4,000 years old who also knew previous wearers of the mask but he is a Psychopathic Manchild who thinks hurting people and playing with their spines is fun which understandably disturbs The Mask.
- The Mask is a cartoonish man who is genuinely insane and even though if he decides not to take his face off and keep it on he is pretty much immortal as he does not age or get killed however he acts and behaves like a kid, has a short attention span of one as he gets easily distracted by trival things, tends to be too strong towards any woman he sees, just wants to have fun and dance at the Coco Bongo but he is a good hearted man who also cares about his friends, the people who live with him in Edge City even if they annoy him at times and does not like hurting people or killing them or even wants to as he finds out that Skillit's idea of fun involves all of those things that he hates and he does put himself back on track once he sees that everyone is in danger which that he even in his most chaotic state of mind will go over and save them all with success.
- Star vs. the Forces of Evil: The Magic High Commission is a council of all-powerful magical beings who govern over the laws and forces of magic, and they have been around for thousands of years. Two of the members in particular, Hekapoo and Rhombulus, don't exactly seem qualified for that responsibility. Rhombulus is a Psychopathic Manchild with a Hair-Trigger Temper, and Hekapoo essentially has the personality of a Bratty Teenage Daughter.
- Steven Universe: Gems are born fully grown then never age, and most of them are thousands of years old. Their level of maturity varies a lot, with some acting very childish, usually looking pretty child-like as well:
- Amethyst is over 5000 years old, yet looks and acts a lot like a teenager. A few decades earlier, she looked and acted more like an 8-year-old. Turns out other Amethysts, despite being physically larger, act just as rowdy as she does. Later subverted, as Steven's influence and the events of the series do inspire her to mature, to the point she ultimately becomes one of the most emotionally stable characters by the end of season five.
- Lapis Lazuli is millennia older than Amethyst, yet has the looks and much of the attitude of a Bratty Teenage Daughter. Other Lazulis share this trait, as shown when Lapis confronts an antagonistic pair of them in the Steven Universe: Future episode "Why So Blue?". They mostly mock her and throw around petty insults, being more of a great annoyance than an actual threat.
- Peridot is an unspecified amount younger than Amethyst, but still thousands of years old. She parrots Steven's Eyelid Pull Taunt, is fond of name calling, and finds slapping other people/gems amusing. When she loses her limb enhancers, it's revealed that she's only about Steven's height, and acts progressively more childlike, even mimicking laser sounds ("Take that, Cluster!) just like a kid.
- Rubies are a caste of disposable grunts, designed for a focus on raw strength over intelligence. Consequently, they're all very lacking in emotional intelligence even Eyeball, who's more serious than the other Rubies (and also the oldest of her squad, and a veteran of the war between Homeworld and Rose Quartz's rebellion over Earth), is impulsive and short-sighted to a dangerous degree. This, along with their short-stature (indicative of their low rank), basically makes them Homeworld's army of immortal munchkin brats.
- Lampshaded in "The New Crystal Gems". Lapis, Peridot and Connie pretend to be the Crystal Gems to do their job while the regular team is in space. When Peridot and Lapis cause damage while fighting over who gets to be Garnet, Connie tries to give one of Steven's speeches, but falls flat on her face. Lapis and Peridot begin to fight and throw insults back and forth, until Connie snaps.
Connie: WILL YOU TWO CAN IT?!
Lapis: That's not a very Steven thing to say.
Connie: I don't CARE! So maybe, I'm NOT Steven! Maybe he's really great at helping people work out these arguments! Maybe he's really patient and caring, even though it must be hard for him having to be the adult for a bunch of SUPERPOWERED CHILDREN!
Lapis: We're both thousands of years older than you.
Connie: THEN ACT LIKE IT!
- Aquamarine looks and acts like a spoiled child but is likely as old as any other gem.
- Pink Diamond, in the flashback dream in "Jungle Moon", acted very much like a Bratty Teenage Daughter and Annoying Younger Sibling to Yellow Diamond, throwing a temper tantrum over not having a colony of her own. She eventually grew up some, but still remained something of a Woman Child at heart even as Rose Quartz. During a moment of vulnerability she tells Greg that she envies humans for how natural it is for them to grow and change.
- Wander over Yonder: While it is unclear if Wander is immortal or just has an extremely long lifespan, "The Waste of Time" shows that he was just as much of a villain-pestering goofball 1000+ years ago as he is today.
- On Young Justice, Klarion is a Humanoid Abomination who is "ageless" yet looks like he might be twelve. He can cause worldwide supernatural chaos in-between bizarre puns, pouting at other supervillains and getting into arguments with his cat, Teekl. Averted by the show's other immortals, Vandal Savage and Ra's al-Ghul, who are both evil but generally more mature.