Extracts work for a feeble youth (7)
I believe the answer is:
milksop
'a feeble youth' is the definition.
(I've seen this before)
'extracts work' is the wordplay.
'extracts' becomes 'milks' (milking is a kind of extracting).
'work' becomes 'op' (common abbreviation for 'opus').
'milks'+'op'='MILKSOP'
'for' acts as a link.
(Other definitions for milksop that I've seen before include "Weakling" , "He shrinks from" , "Feeble male" , "Unassertive male person" , "soft fellow" .)