Youth voices entertaining panto when in cast (5,4)
I believe the answer is:
salad days
'youth' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for salad days that I've seen before include "Period of youth and inexperience - on lettuce diet?" , "Carefree youth" , "Period of youth and inexperience - ate lettuce dishes?" , "musical" , "Time for a vegetarian diet" .)