Did something about rearing delinquent youth (5)
I believe the answer is:
acted
'did something' is the definition.
('act' can be a synonym of 'do something')
'about rearing delinquent youth' is the wordplay.
'about' becomes 'ca' (circa).
'rearing' says the letters should be written backwards (as in a horse rearing up).
'delinquent youth' becomes 'ted' (member of the Teddy Boy subculture).
'ca' back-to-front is 'ac'.
'ac'+'ted'='ACTED'
(Other definitions for acted that I've seen before include "Played a role" , "Played a 30ac" , "Play a role" , "produced an effect" , "Behaved or performed" .)