Boy conceals desire to be a medic (7)
I believe the answer is:
surgeon
'a medic' is the definition.
(I know that surgeon is a type of Dr.)
'boy conceals desire' is the wordplay.
'boy' becomes 'son' (synonyms).
'conceals' indicates putting letters inside.
'desire' becomes 'urge' (I've seen this before).
'son' enclosing 'urge' is 'SURGEON'.
'to be' acts as a link.
(Other definitions for surgeon that I've seen before include "Hospital worker" , "Doctor with a scalpel" , "Doctor with cutting tools" , "One operating in theatre" , "Medical specialist" .)