Adult allowed to wear the jumper, perhaps (7)
I believe the answer is:
athlete
'jumper perhaps' is the definition.
(jumper is a kind of athlete)
'adult allowed to wear the' is the wordplay.
'adult' becomes 'a'.
'allowed' becomes 'let' (I've seen this before).
'to wear' means one lot of letters goes inside another.
'let' going inside 'the' is 'thlete'.
'a'+'thlete'='ATHLETE'
(Other definitions for athlete that I've seen before include "E.g. runner or jumper" , "The late one is very fit, oddly" , "Eg, a runner or gymnast" , "Contestant" , "Sporty type" .)