I would hate to be the one to pluck out the heart of Peter’s mystery, but happily I would be quite unable to do so even if I wanted to, since Peter is a paradox! "Who is Peter?" asks Barrie in his silent screenplay of Peter Pan (1920) - "Perhaps he is just a boy who died young." This is an echo of something Barrie wrote 12 years earlier, in the production notes for the Paris production of "Peter Pan" in 1908: "Of Peter himself you must make what you will. Perhaps he is a boy who died young, and this is how the author conceived his subsequent adventures. Perhaps he is a boy who was never born at all, a boy whom some people longed for but who never came. It could be that those people hear him at the window more clearly than children do."
So, is Peter based on Barrie’s elder brother David, who died aged 13 when Barrie was 6? Or is he Timothy, the dream child Barrie longed for in “The Little White Bird”? Or both? Or neither?
Or is he Barrie himself, in some sense “rejected” as that 6 year old by his mother? “Oh Wendy, you are wrong about mothers! I thought like you about the window, so I stayed away for moons and moons, but when I flew back the window was barred. My mother had forgotten all about me, and there was another little boy sleeping in my bed.” Perhaps this is why Barrie originally called Peter Pan “the Boy Who Hated Mothers” ...
One final paradox, from the published play of "Peter Pan":
Peter: I never want to grow up! I just want always to be a boy and have fun!
To which Barrie has added in the stage directions: “So perhaps he thinks, but it is only his greatest pretend.”