If "Peter Pan" is about a bou who would not grow up, "Tommy & Grizel" - written by Barrie 4 years earlier in 1900 - is about a boy/man who could not grow up. I quote a good deal from it in my biography JMB&TLB, and there are plenty of copies to be had on the internet, e.g. abebooks.com. But immaturity and not growing up are not the same thing in my view... although it would take a thesis to explain myself! I'll post your enquiry on the Anon website in case anyone wishes to chip in their tuppence worth. Good luck, and feel free to post any further thoughts or questions on this forum.