Large whisky maybe for young singer? (6)
I believe the answer is:
treble
I believe this clue is a double definition.
'large whisky maybe' is the first definition.
(drink with three shots)
'young singer?' is the second definition.
(young male singing voice)
'for' is the link.
(Other definitions for treble that I've seen before include "What boys sing" , "Soprano - multiply by three" , "Score of sixty with one dart?" , "High-frequency (radio control knob)" , "Choirboy" .)