In a sense old, but no veteran (7)
I believe the answer is:
vintage
'sense old but no veteran' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'in a' is the wordplay.
I cannot really see how this works, but
'in' is present in the answer.
'a' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for vintage that I've seen before include "High-quality wine" , "classic" , "Wine of a good year" , "Old" , "Wine harvest" .)