Sorry for not being consistent, but I thought third person would fit Peter better. This was based on one sentence I read on Neverpedia (yes, I'm a total fangirl), "In Peter and Wendy it is explained that Peter must forget his own adventures and what he learns about the world in order to stay child-like." So here it is!
Peter Pan had many adventures. But every time he had a new one, he must trade in a memory of an old adventure, or else he would grow up. Too many experiences caused you to grow up, and to grow old. Forgetting old experiences left you childish and naïve, and kept you from growing up. Peter had no problem with this at all until one girl entered his life, and he had the most amazing adventure.
Peter refused to forget the girl, though it was inevitable. He couldn't help having more and more adventures. But through it all, he held onto the memory of this girl. Slowly, though, ever so slowly, she began to fade anyway. What was her name? He couldn't, for the life of him, remember. Why did he want so desperately to remember her anyway? He honestly did not know. But he remembered her face, the way it lit up when… Was that all he could remember? It couldn't be, it just couldn't! But it was.
Even this tiny bit of his past cost him a lot. Eventually, he began to grow up. Much slower than any normal boy, but it was undeniable. His voice became deeper, and he grew taller and taller... All because of this girl! Too many times he had contemplated letting go of the memory, but something stopped him. She was much more important than staying young forever. She was… She was his Wendy-lady.
The more he remembered, the faster he grew. Wendy had wanted to grow up! She had wanted him to grow up too… Would she be happy now? He was growing, and because of her, too! He wanted to visit her, tell her that he was ready to grow up with her, but soon, he learned that he could no longer fly. Where was the fun in staying in Neverland forever if he was grown up?
So he did the only thing he could do. He forgot his Wendy-lady, learned to fly, and became a child once more. Perhaps it was better this way anyway, for, Peter did not know it, but by this time, Wendy was long dead.