Youth speaks about panto, dropping in (5,4)

I believe the answer is:

salad days

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'youth' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for salad days that I've seen before include "Carefree youth" , "Period of youthful inexperience" , "musical" , "Time for a vegetarian diet" , "when one is young?" .)

I've seen this clue in The Guardian.

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