Why is Holden Caulfield afraid of the world and growing up?

The thing is, Holden wants to stay young forever. He doesn't want to grow up. He also wants to protect kids from growing up. I think Allie's death does have a little bit to do with it because he wont get older. You can tell based on many of the symbols in the book, that Holden wants to stay young. He loves the museum because nothing changes. He hides and isolates himself because he is afraid of adulthood. He fears the many responsibilities, becoming ually active, etc. He just isn't ready to grow up yet.