Dad on bass held back music of his youth? (7)
I believe the answer is:
britpop
'music of his youth?' is the definition.
(music genre)
'dad on bass held back' is the wordplay.
'dad' becomes 'pop' (synonyms).
'on' means one lot of letters go next to another.
'bass' becomes 'b' (musical abbreviation).
'held back' becomes 'rit' (short for ritardando, musical instruction).
'b'+'rit'='brit'
'pop' after 'brit' is 'BRITPOP'.
(Other definitions for britpop that I've seen before include "1990s popular music style" , "music genre" , "Guitar music of the '90s" , "Mid-1990s' music of Oasis and Blur" , "Blur, Oasis et al" .)