History Main / ImmortalImmaturity

* Edward and his siblings from ''Literature/TheTwilightSaga''. 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.

* The 3.5 edition [[TabletopGame/DungeonsAndDragons 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.

* Subverted in the ''TabletopGame/{{Ravenloft}}'' supplement ''Van Richten's Guide To Vampires'', which proposes that vampires go through a psychological maturation process that ''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 ''TabletopGame/VampireTheRequiem'' and ''TabletopGame/VampireTheMasquerade'' 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 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.

* [[Characters/GravityFallsBillCipher Bill Cipher]] of ''WesternAnimation/GravityFalls'' 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." [[{{Foil}} This helps highlight the show's]] ComingOfAgeStory, especially as the last few episodes juggle Bill's invasion with the twins trying to define themselves as they reach teenagehood.

** 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. [[spoiler:Turns out other Amethysts, despite being physically larger, [[PlanetOfCopyhats 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 BrattyTeenageDaughter. Other Lazulis share this trait, as shown when Lapis confronts an antagonistic pair of them in the ''WesternAnimation/StevenUniverseFuture'' 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 EyelidPullTaunt, 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.

** Pink Diamond, in the flashback dream in [[Recap/StevenUniverseS5E12JungleMoon "Jungle Moon"]], acted very much like a BrattyTeenageDaughter and AnnoyingYoungerSibling to Yellow Diamond, throwing a temper tantrum over not having a colony of her own. [[spoiler: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.]]
** White Diamond is the most mature and composed of the Diamonds, but [[spoiler: when her ControlFreak nature is resisted, she quickly loses her cool and shows off how immature she can be about it. Having her childish tantrum pointed out to her by Steven (after she yelled at him for acting like a child and he responded [[ArmorPiercingQuestion "I am! What's your excuse?!"]]) immediately causes her HeelFaceTurn by shattering her delusion of being a perfect eternal being.]]

** The Ice King's behavior is wholly the result of his [[ArtifactOfDoom 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.

* [[BewareTheSillyOnes Bill Cipher]] of ''WesternAnimation/GravityFalls'' 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." [[{{Foil}} This helps highlight the show's]] ComingOfAgeStory, especially as the last few episodes juggle Bill's invasion with the twins trying to define themselves as they reach teenagehood.

** [[GodOfEvil Discord]] is far older than even the millennia-old [[TheHighQueen Princess]] [[GodEmperor Celestia]], but as [[AnthropomorphicPersonification the spirit of chaos]] is only concerned with spreading his concept of fun and excitement. He's also an [[TheOmnipotent omnipotent]] RealityWarper with a passion for [[CorruptTheCutie psychological]] [[BreakTheCutie torture]]. Not a good combination. [[spoiler: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 HairTriggerTemper, is prone to mood swings, and [[OneOfTheKids seems to get along better with children than adults]]. On the other hoof, she takes to her responsibilities with pride and dedication.

* ''WesternAnimation/StarVsTheForcesOfEvil'': 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 PsychopathicManchild with a HairTriggerTemper, and Hekapoo essentially has the personality of a BrattyTeenageDaughter.