Upcoming artist mostly past his prime (4)
I believe the answer is:
aged
'past his prime' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'upcoming artist mostly' is the wordplay.
'upcoming' says the letters should be written in reverse (in a down clue coming up is backwards).
'artist' becomes 'Degas' (painter Edgar Degas).
'mostly' means to remove the last letter (most but not all of the word).
'degas' with its last letter removed is 'dega'.
'dega' written backwards gives 'AGED'.
Can you help me to learn more?
(Other definitions for aged that I've seen before include "Got older" , "Long in the tooth" , "Advanced in years" , "Matured like wine in wood" , "Like Uncle Arly" .)