Juvenile going up to claim benefit (10)
I believe the answer is:
adolescent
'juvenile' is the definition.
(synonyms)
'going up to claim benefit' is the wordplay.
'going up' becomes 'ascent' (ascending means going up).
'to claim' means one lot of letters goes inside another (inserted letters are claimed or taken in).
'benefit' becomes 'dole' (informal term for a state benefits).
'ascent' placed around 'dole' is 'ADOLESCENT'.
(Other definitions for adolescent that I've seen before include "Youth" , "Developing" , "juvenile" , "sixth-former, say" , "One growing" .)