An old person's skill in bridge (7)
I believe the answer is:
spartan
'an old person's' is the definition.
The answer and definition can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'skill in bridge' is the wordplay.
'skill' becomes 'art' (both can mean a talent).
'in' means one lot of letters goes inside another.
'bridge' becomes 'span' (synonyms).
'art' placed within 'span' is 'SPARTAN'.
Can you help me to learn more?
(Other definitions for spartan that I've seen before include "Of conditions, simple and harsh as for ancient Greeks" , "Without comforts" , "Austere - disciplined" , "Indifferent to luxury" , "Very strict - austere" .)