Nobleman with youth leader ahead of time (5)
I believe the answer is:
early
'ahead of time' is the definition.
(synonyms)
'nobleman with youth leader' is the wordplay.
'nobleman' becomes 'earl' (member of the nobility).
'with' means one lot of letters go next to another.
'youth leader' becomes 'y' (I've seen this in other clues).
'earl'+'y'='EARLY'
(Other definitions for early that I've seen before include "before anyone else?" , "Gothic style following 13" , "Advanced" , "Before the ETA" , "Before appointed time" .)