Basic Trope: An adult character who acts like an exuberant little kid.
Straight: Bob is in his 30s, yet still acts like an 10-year-old. He plays with toys and he loves candy.
Exaggerated: Bob is nearly 100 years old, and yet he behaves like an infant.
Downplayed: Even though Bob has some childlike interests, he acts like an adult if the situation calls for it.
Bob didn't have much of a childhood, and is reliving it in his adult years.
Bob has grown up around very immature people.
Bob has a developmental disability.
Bob is a character in a Work Com set at a toy store, and he believes playing with the toys makes him a better worker.
Bob was in a coma at the age of 10 to 30.
Bob recognizes that "grown-up" society isn't nearly as mature as it makes itself out to be, so he decides he'll just enjoy himself with his toy soldiers and not worry about being seen as childish by the guys that ask their leaders to send real-life flesh and blood soldiers to their very real deaths for some stupid, childish reason.
Growing older is mandatory, growing UP is optional.
Inverted: Bob is an 10-year-old who acts like a 30-year-old.
Subverted: Bob starts acting his age.
Double Subverted: He was only acting like that for a job interview.
Parodied: Bob even dresses like an 10-year-old.
Zig Zagged: Bob starts acting his age. But that was just for a job interview. But even after he gets the job, he starts acting more mature.
Averted: Bob acts his age the whole time.
"We need a grownup who acts like a little kid. This is a comedy show, after all."
An Aesop describing how growing up is optional, whereas growing older is mandatory.
Lampshaded: "How old are you?" "Physically 30, psychologically 10."
Invoked: Bob is thinking back to his childhood and remembers how unpleasant it was. Then he gets some ideas...
Defied: Bob decides that even though his childhood was unhappy, he'll just work harder to have a pleasant adult life.
Discussed: "I don't want him around our children. He's giving them the wrong idea...in more ways than one".
Conversed: "Oh, geez, another adult who keeps acting like a kid. Oldest trick in the book".
Implied: Alice talks about her Uncle Bob who is never seen by the audience and mentions how much he loved playing with toys and making fart sounds.
Deconstructed: Bob's attempts to relive his childhood indicate some serious psychological problems on his behalf. He's never able to mentally "grow up" and remains distrusted by both adults and children alike.
Even though Bob is trying to relive his childhood, he still knows when to act like an adult, so there are no problems.
Growing older is mandatory, but growing UP is optional, and people still manage to accept him for who he is.
Played For Laughs: Bob is a character in a zany comedy and his antics are meant to be funny and endearing.
Played For Drama: Bob's behavior means he is unable to make friends or have a deep relationship and, since he has no ability to rationalize the consequences for his actions, regresses even farther into his manchild state.
Oh boy, oh boy, oh boy! I can't wait to go back to Manchild!