Other mistake: When the pirates are thrown off the boat by Peter, after being kissed by Wendy, the splash is not heard and they cannot be seen in the water when Peter flies up into the air.
Other mistake: At the very end of the movie, Peter says "to hear stories about me" and we see Wendy and her eyes are moving as if watching him fly away, but when it cuts back to Peter he then starts to fly away.
Continuity mistake: In the scene in the black castle where Hook is about to kill Peter he cuts Pan in the chest with his hook, in the next shot the cut is gone.
Other mistake: In the scene where Wendy admits to being Red-Handed Jill, Tootles says "Mother and Father are fighting again" and Curly is mouthing his lines.
Continuity mistake: When Peter & Wendy go to see the mermaids, one of the mermaids places her hand on top of Wendy's, and starts to put her head underwater. In the next shot (filmed from behind the mermaid), before Peter hisses at it, she is upright in the water, not dipping her head under anymore.
Continuity mistake: When Hook makes Wendy tell the story of Peter Pan and subsequently shoots Noodler, the first of the two pirates to go down at storytime, the camera cuts to the next shot and Hook's pistol is out of his hand, which is not only visible, but being held up in the air, as opposed to under his right arm where he shot from.
Continuity mistake: When Wendy walks between John and Michael's beds, you can see John and Michael sleeping, but when Wendy asks Peter if John and Michael can come too, in the next shots of John and Michael, their sleeping positions have suddenly changed.
Answer: It's not that you never age, it's that you never grow up, i.e. pass into puberty and become an adult.
Myridon