Youngster about to press for the operator (7)
I believe the answer is:
surgeon
'for the operator' is the definition.
(I've seen this in another clue)
'youngster about to press' is the wordplay.
'youngster' becomes 'son' (a child).
'about' means one lot of letters goes inside another.
'to press' becomes 'urge' (synonyms).
'son' enclosing 'urge' is 'SURGEON'.
(Other definitions for surgeon that I've seen before include "Medical man" , "Operating medical practitioner" , "Naval doctor" , "one used to working in the theatre" , "Medical practitioner - go nurse (anag)" .)