I would say he probably didn't "want" to grow up. It's just so much to do as an adult and their are plenty of responsibilties to take. Peter just wanted to have fun and not do adult things. Sometimes i don't want to grow up either l0l.
I believe that deep in the heart of the character Peter Pan, he wanted to remain a child because of his mother. When he left it was because he was so afraid of being an adult and having so many responsibilities. Being so young, the thoughts overwhelmed him. So he left home but one day realized that as all children do he missed his mother very much. However upon the return to his home, he found his mother had yet another child. This sparked pain that maybe he'd be unwanted and caused him to leave once more. Deep in his heart he longed to be the child that his mother rocked to sleep at night and protected from all the bad things in the world. He wanted to be free of responsibility so strongly that perhaps some where in all the magic, this wish too was granted and so a child he remained. When a child is robbed of their childhood they can never truly grow up and even as adults remain in a childish state of mind.
I thought he wouldn't grow up as opposed to couldn't but either way I figure it is a metaphor.
As a metaphor you can look at it a couple of ways.
One would be the refusal to mature and accept responsibility unless forced to. A condition many adults have now and probably did back when the character was created written in 1902.
The other would be Peter is embracing his inner child. A theme that was fairly central to the Finding Neverland movie where Robin Williams became so 'adult' at first he couldn't even remember Neverland.
Of course there is always, "Cuz that's the way the author wrote it!" smile
I've always wondered this, and want to know other people's opnions.
I've read teh J,M Barrie book, but I don't remember it ever actually disclosing it.
If you're looking for a literal, physical reason in the book, you're not going to find it. But if you pay attention to the themes and subtext, you'll see it: in the book, the aging process is essentially a natural side effect of maturing and progressing as a person. However, Peter refuses to progress and grow as a person - because that would mean accepting pain and responsibility - and as a result remains forever frozen in time. The book makes it clear that this is a bittersweet situation, because while he is functionally immortal he ends up forgetting everyone he ever knew. Furthermore, the only form of love he can feel is that of a child toward a mother, which is a selfish rather than selfless form of love.
Adults can also refuse to move on in this world, too. While Captain Hook's age is never explicitly made known, it's revealed that he was contemporary with Barbecue, or Long John Smith. This would mean that Hook was alive in the middle of the 18th century, whereas the book is set in the early 20th century. Hook's own miseries and demons are linked to his refusal to move on emotionally - he is obsessed with getting vengeance on Peter, and he lives in constant fear of the crocodile. He only escapes his misery when he gives up on his revenge and embraces the final change - death - by jumping into the jaws of the crocodile.