Leap over coward as youngster (6,7)
I believe the answer is:
spring chicken
'youngster' is the definition.
(I've seen this before)
'leap over coward' is the wordplay.
'leap' becomes 'spring' ('spring' can be a synonym of 'leap'**).
'over' is a charade indicator (letters next to each other).
'coward' becomes 'chicken' ('chicken' can be similar in meaning to 'coward').
'spring'+'chicken'='SPRING CHICKEN'
'as' is the link.
(Other definitions for spring chicken that I've seen before include "Young (bird or) person" , "Young person (as seen by an old person)" , "Fowl - type of youth" , "Young bird (used as disparaging comparison with older people)" , "Youngster" .)