Jasmine's father, the sultan, from Aladdin. At times he acts very childish, such as collecting toys and getting really excited when riding the carpet. To be fair, at times Jafar is magically controlling the sultan. Things get better when Aladdin breaks Jafar's staff.
Humphrey from Alpha and Omega has signs of this. Matures out of it by the sequel.
"Baby Brent" certainly comes across as one. He's the same age as Flint, doesn't seem to be doing anything with his life besides being popular, and still acts like a schoolyard bully. That he still reenacts the commercial he appeared in as a baby, diaper and all, seems to be a serious case of Lampshade Hanging.
And on the other hand there's Flint himself, who put fake security equipment in his lab and pretends to use it when he comes and goes. Even the kids in the neighborhood think he's weird.
Frozen: Princess Anna, due to being cooped up in the castle for so long. Downplayed as she's only eighteen.
The Tie-In NovelA Frozen Heart reveals that except for Lars, most of Prince Hans' 12 older brothers have become this because their father, the king of the Southern Isles, has spoiled them too much. Caleb is the worst of all, as being the heir and the king's favorite son transformed him into a RoyallySpoiled Brat, blatantly ignoring his family by seeking his father's attention and treating the idea of running a kingdom as a toy or having a brawl with his brothers at the stables. Hans often saw most of his brothers as immature men, as they often picked on him for being the youngest of the large Westergaard clan.
Sid from Ice Age so very, very much! Remember the time he got worried about what Santa Claus thinks?
Pleakley has a very childish fascination with the cultures of earth as he reacts with childish glee over studying things such as rocks or holidays. In one episode of the series it is revealed that he eats sugary cereals for breakfast. His voice also sounds childish on occasion.
Gantu also has some traits of this. Despite being a hulking, authoritative brute, Gantu was revealed to enjoy bubble baths and he even plays with bath toys and reenacting battle scenes with the toys in a childish way.
Timon & Pumbaa and the Hyenas act a lot like children most of the time.
Scar is this to some extent, too, though at the beginning it's more subtle. However, as he becomes king, he acts like a toddler, as he continuously throws temper tantrums when he doesn't get what he wants or when the other animals upset him. He, in fact, starts to act even more immaturely than the hyenas, Timon & Pumbaa, and the actual kid characters do in the movie as he becomes king.
Batman from The LEGO Batman Movie acts far more immature than his comics counterpart, such as throwing a fit when Alfred reminds him he has to attend Jim Gordon's retirement party and generally refusing to do anything that isn't completely centered around him. Alfred even reads a book on parenting spoiled children when dealing with Batman, just to drive the point home.
Quasimodo from The Hunchback of Notre Dame is also shares some of these traits as he plays with wooden toys, going as far as replicating a miniature version of medieval Paris out of wooden models. He even talks to gargoyles with others thinking that he is delusional in doing this and he is very enthusiastic on going to the festival of fools much like a child would. Unfortunately very justified given he was raised by an abusive and hypocritical judge who killed Quasimodo's mother and has his father arrested and he was forced to stay in the Norte Dame church for twenty years, preventing him from interacting with other people.
Po from Kung Fu Panda is one of those. He is in his 20's and is a master of Kung Fu but he is very immature as he takes bubble baths and plays with action figures (granted, ones he made himself.)
Waffles, the horned toad from Rango, has a childlike personality and matching intelligence.
Tow Mater from Disney Pixar Cars franchise. He's very childlike and childish. Even though he's 60 years old, he literally has the emotional and mental capacity of a 7 year old child. He has a lot of traits of a child. He's enthusiastic, optimistic, cheerful, loyal to a fault and he's very sweet like a child. He's also incredibly playful and friendly like a child too. His emotions are that of a child because when he gets angry, his anger only lasts for a couple of seconds. All of his emotions last only for a couple of seconds and he has genuine yet simple emotions. He probably thinks exactly like a child too. He doesn't think like an adult would. He's a very innocent person.
Prince John from Disney's Robin Hood. He's very whiny, often throws temper tantrums, constantly sucks his thumb and cries very easily.
Prince Charming from Shrek 2. It's the result of being under the thumb of his domineering mother, the Fairy Godmother.
Benjamin Clawhauser from Zootopia is a police officer, yet he eats sugary cereals for breakfast, squeals like a little girl, and can be childishly oblivious at times.
Implied of "The Man Upstairs" a.k.a Finn's Dad, the owner of the LEGO sets the main characters originate from in The LEGO Movie. He's not a stereotypical depiction of the trope, but he does own a lot of LEGO and, when pressed that the age on the boxes indicates that they're children's toys suitable for those between the ages of 8 and 14, defensively responds thus:
The Man Upstairs: That's just the recommended age. They have to put that on there.
Steve Stifler in the American Pie series. Especially in Reunion.
The title character in both versions of Arthur, thanks to wealthy upbringing and a multi-million dollar inheritance, has never needed to hold down a job and is now The AlcoholicFun PersonifiedTabloid Melodrama shame of his by-and-large humorless family as an adult. While he uses his money to enjoy very adult activities, his townhouse also has various childhood pleasures (a giant model train set, a pinball machine, etc.) in the 1981 original, and in the 2011 remake his Establishing Character Moment is a joyride with his chauffeur in the Batman Forever Batmobile. His valet has become his Parental Substitute on top of all this. Ultimately, falling in love with a working-class woman and the threat of losing his money if he chooses her over an Arranged Marriage forces him to gain some measure of maturity to find true happiness (more so in the remake, where the original saved further Character Development for the sequel). The trope is more pronounced in the 1981 original because Dudley Moore was 46 at the time, whereas the remake's Russell Brand was 34. The Expository Theme Tune that appears in both versions discusses this: "Arthur he does as he pleases/All of his life he's mastered choice/And deep in his heart/He's just, he's just a boy".
The title character of Baby Doll, an Innocent Fanservice Girl who is also as obnoxiously emotional as a child. She even still sucks her thumb. However, being the underage bride of a man twice her age has made her more cynical and disillusioned than most examples. Plus, she consciously represses her own sexuality.
Daisy Kensington from Barefoot was raised in isolation (by a schizophrenic mother), and everything she knows about the outside world comes from watching TV. When her mother dies, Daisy winds up in a mental hospital, but the film's protagonist breaks her out and winds up having to teach her how to drive, how to flush an airline toilet, that it's not good manners to go to a strip club and dance on stage with the strippers, etc.
Selena Kyle in Batman Returns starts out as a downplayed version of this. Unlike most examples she lives independently, holds down a job and generally acts like an adult, albeit very timid and insecure. However, her home is bright pink and cutesy and she's shown to own dozens of stuffed animals and a dollhouse.
Chance the Gardener in Being There; in the movie version his maid Louise actually says "You're always gonna be a little boy, ain't cha?" when she leaves after the death of the master of the house. It's stated in the book and heavily implied in the film that he is mentally challenged; the twist is that most of the other characters don't recognize this, making the character a Trope Namer for similar mistaken identity situations. Peter Sellers played him in the film; he initiated its making because he identified with the character so strongly when he read the book. For better and worse, he was a Real Life example of this.
Josh Baskin comes off this way in Big, he really is a 12-year-old boy in the body of an adult due to a wish he made to become taller so he could ride a roller coaster at the carnival. It gets Squicky when, in an attempt to prove to his mother he's really her son despite having a 30-year-old's physique, he briefly pulls down his pants to show her his little-boy underwear, and she naturally freaks out.
When the two of them aren't killing gangsters, Connor and Murphy McManus, The Boondock Saints, are prone to bickering and tussling like ten-year-old boys.
Both John and Dean Solomon from The Brothers Solomon.
Billy from Buffalo 66 is gradually revealed to be this. He doesn't like girls, he makes up bizarre stories, he bullies his friend, and is naive enough to get in trouble with gamblers.
In another Burton flick, Charlie and the Chocolate Factory, is Willy Wonka, who comes off as eerily similar to Pee-Wee Herman in this adaptation. But while Wonka appears to be completely unselfconscious of what a manchild he is (at one point in the film, he argues that he was never as small as a child, because he remembers being able to reach his head to put a hat on top of it), unlike in Herman's world other people notice and are more than a little squicked by him.
Fatty Arbuckle in many of his films. In Coney Island, he is introduced at the beach, shoveling sand into a plastic bucket with a toy shovel.
Buddy from Elf is over 35 years old and still acts like a six-year-old and has a very infantile view of the world; this is due to being raised by elves from infanthood; Buddy even notes that he doesn't know many other people who "share my affinity for elf culture."
In the American version of Fever PitchJimmy Fallon's character is called a manchild by his girlfriend, but all-consuming passion for the Red Sox aside he's a comparatively mild example: he's good with women, has a job as a well-respected junior high math teacher, and he has his own apartment.
In Finding Neverland, James Barrie is (mostly) capable of taking care of himself, but he has an air of immaturity and childlike wonder about him, and he clearly has much more fun playing make believe with the Llewelyn Davies boys than he does socializing with adults.
Jeff from Grandma's Boy (2006): he's over 30 years old and still lives with his parents, he wears footy pajamas, he sleeps in a racecar bed with many stuffed animals while sucking his thumb, and spends most of his time playing video games.
Park Gang-du from The Host is the "lovable innocent" variation. He's upbeat, cheerful and good at heart, but he's a clueless and irresponsible single parent who lives with and works for his father. His siblings are constantly annoyed with him and the only one who understands him is his father. He finally matures, however, and reveals a fierce Papa Wolf side to him.
Marv from Home Alone is very childish at heart, contrasting Harry who's more overtly serious. His number one priority from the stolen houses are the toys and people's snow globes for his collection, and he floods their victim's houses because they're "The Wet Bandits" and "all the great ones leave calling cards". Needless to say he still manages to be every bit as violent and dangerous as Harry as he's fully willing to torture and kill Kevin, to the point he'd be a full-on Psychopathic Man Child if he wasn't so Affably Evil when not otherwise pressed.
Sam from I Am Sam, although he actually is mentally retarded. It's stated early in the film that he has the intellectual capacity of a seven-year-old.
Inverted with the titular character in Jack due to accelerated aging. Jack seems like this, but he's not a man who acts like a child, he actually is a child and looks like a man.
James Bond: More so than any other actor in the franchise, Pierce Brosnan placed greater emphasis on his character being an emotionally stunted man. Bond fears commitment in a romantic relationship because he abandons his girlfriend Paris when he realizes that he's falling in love with her. Witness his childish glee as he "drives" his remote-controlled car during the multi-level parking lot chase scene. After Wai Lin compliments him on his motorcycle skills, his reply invokes this trope: "Well, that comes from not growing up at all." M describes his brand of charisma as "boyish," and Q says "Grow up, 007!" twice in exasperation. Alec asks Bond, "Why can't you just be a good boy and die?", Natalya accuses him of being "boys with toys," and Jinx scoffs, "You're a big boy; I figured you could handle yourself." M even vaguely serves as a maternal figure towards Bond, which further emphasizes his immaturity.
Justin from Kickin It Old Skool, this is justified as he was in a coma for 20 years.
Marie Antoinette portrays Louis XVI as this way in his youth. He's awkward around Marie and obsessed with his hobby of locks. He doesn't try to consummate until months or years after their marriage, when it seems that the mechanics of sex are explained to him.
Johnny Boy in Mean Streets seems to be emotionally and mentally stuck at age 14.
The main characters of Mystery Team are a group of "Kid Detectives" who still continue their exploits even though they're in their late teens and still having the mental age of seven. They are hired by a girl to solve her father's murder.
Pain and Gain: Paul acts like a big kid at times. This is actually what makes him the most sympathetic of all three protagonists.
Paul Reuben's character Pee-wee Herman in Pee-wee's Big Adventure and Big Top Pee-wee. He seems to be an adult man who never grew up. He lives in his own house filled with toys. He has a girlfriend in each film, but shows a prepubescent lack of interest in them. He even has another Man Child rival. Other characters frequently refer to him as a "boy", though this could be just arrogance or condescension on their part.
Both Sam and Ludlow in Pixels, although Ludlow is a more severe example: in his thirties, he has no job, lives with his grandma, has a Stalker Shrine of a computer game character and spends his time making conspiracy theories over the internet.
Dewey played by Jack Black in School of Rock is an immature rocker who has no life outside of rock. It helps him to find common ground with the kids.
Normally he's The Stoic and a genuinely intimidating presence but upset The Force Awakens's Kylo Ren (who's like 30) and he'll slash up everything in his vicinity in a violent rage while screaming like a banshee.
Harry Langdon's comic persona. In The Strong Man, his character is utterly terrified when a woman makes what he thinks is a sexual advance (she's really trying to pick his pocket). He's similarly horrified by the sight of a nude model in an art studio. In general, he behaves with childlike innocence.
The protagonist in Teddy Bear is 38 years old and lives with his mom. They even share the bathroom.
Thor and Loki are both mild examples in Thor. They're centuries-old alien demigods played by actors in their late twenties, but Thor starts out behaving like a frat boy (he improves with Character Development), and Loki, for all his cleverness, has the apparent emotional maturity of a melodramatic teenager (not to mention the daddy issues).
TRON has Kevin Flynn, who seems to have regressed to this state after getting kicked out of his company. When we first see him, he's the owner of an arcade and wowing his teenage customers with his virtuoso game skills. His office overlooks the arcade, Lora (his ex) shouts in frustration "Now, you see why all his friends are fourteen years old!"
Gary King from The World's End is an idiot who still acts and dresses as he did as a teenager.
Deconstructed. Gary was the coolest kid in school (or at least he thinks he was), and because of this, he hasn't moved away from his teenage persona. His hedonistic partaking of drugs and alcohol is an attempt to move away from the reality of his miserable existence, and his inability to drop his teenage pursuits as he approaches his forties is seen as more pathetic than charming. According to Word of God, Gary is meant to draw parallels with people who attend their 20th/25th high school reunions and find that they have accomplished very little with their lives. Reconstructed in that with his view of himself, he is much happier as a sword-wielding hero in the post-apocalyptic, pre-industrial world he creates by rejecting The Network.
In The Wrestler, the main character is one, and it's shown in a tragic, negative light.
X-Men: Days of Future Past: The younger Charles Xavier rejects all adult responsibilities after he succumbs to depression, and McCoy has to look after him.
X-Men: Apocalypse: At the age of 27, Quicksilver still isn't an independent adult because he continues to reside in his mother's basement, although his living space is a lot less cluttered than it was in Days of Future Past, which implies that his kleptomania has toned down in the past decade. He cracks a joke about his mother wanting him to get out of the house, and Peter acknowledges his Basement-Dweller status during the jet ride to Cairo.
Played with in The 40-Year-Old Virgin; the main character is, as the title suggests, not sexually active, and also dresses in a rather buttoned-down fashion, has a typically childish hobby of collecting comic-book action-figures and is slightly naive and inexperienced, coming across on the surface as being one of these. However, on the whole he's actually managed to get his shit together a lot more successfully than many of the supposedly more 'experienced' men and women around him, and generally comes off as being a lot more mature, well-rounded and wise about life than them.
Generally speaking, all characters in Judd Apatow films can be divided between adult children and tightwads.