The girl is captivated by youngster, one with wings (6)
I believe the answer is:
cherub
'one with wings' is the definition.
(type of angel)
'the girl is captivated by youngster' is the wordplay.
'the girl' becomes 'her' ('her' refers to a girl or woman).
'is captivated by' means one lot of letters goes inside another.
'youngster' becomes 'cub' (I've seen this before).
'her' inserted inside 'cub' is 'CHERUB'.
(Other definitions for cherub that I've seen before include "Member of heavenly group" , "Angel portrayed as a winged child" , "Angelic baby" , "A heavenly winged child" , "innocent-looking child" .)