Why did Peter Pan not want to grow up?

Because he wanted to always be a boy and to have fun. He said that "if to grown means it will be beneath my dignity to climb a tree, then I will neve grow up, never grow up, not me!"
Peter refuses to grow up. As a baby he heard his parents talking about how he would grow up and work in an office, and he didn't like the sound of that, so he flew out the window to live with the fairies in Kensington Gardens, and then in Neverland. I have been there... he told me :)
He couldn't have grown up, simply because he was a fictional character ( possibly based on a true person, but fictional none the less).

Possibly Word your questions in a manner which are relatively coherent as-well...