Youngster to receive support, it's settled (4,2)
I believe the answer is:
paid up
'settled' is the definition.
(paying up is a kind of settling)
'youngster to receive support' is the wordplay.
'youngster' becomes 'pup' (I've seen this in other clues).
'to receive' is an insertion indicator.
'support' becomes 'aid' ('aid' can be a synonym of 'support'**).
'pup' placed around 'aid' is 'PAID-UP'.
'it's' acts as a link.
(Other definitions for paid up that I've seen before include "without arrears" , "finally settled" , "Fully committed" , "Debt-free" .)