The boy who never grew up (5,3)
I believe the answer is:
peter pan
'the boy who never grew up' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for peter pan that I've seen before include "Barrie's youthful hero" , "Child that never grows old" , "J. M. Barrie play" , "J M Barrie's ever-young boy" , "Kind of collar for" .)