In middle age romancer is keen (5)
I believe the answer is:
eager
'is keen' is the definition.
(I've seen this before)
'in middle age romancer' is the wordplay.
'in' says the answer is hidden in the clue.
'EAGER' is hidden within 'middle age romancer'.
(Other definitions for eager that I've seen before include "Keen (as a beaver?)" , "Swiss mountain" , "Excited by desire" , "Like some beavers" , "Anxious" .)