Agree with a lofty youth leader (5)
I believe the answer is:
tally
'agree' is the definition.
(synonyms)
'with a lofty youth leader' is the wordplay.
'with' is a charade indicator (letters next to each other).
'a lofty' becomes 'tall' (I've seen this before).
'youth leader' becomes 'y' (I've seen this in other clues).
'tall' next to 'y' is 'TALLY'.
(Other definitions for tally that I've seen before include "highly?" , "Square" , "Mark" , "Agree - count" , "Coincide" .)