Mean to declare advancing years? (7)
I believe the answer is:
average
'mean' is the definition.
(synonyms)
'declare advancing years?' is the wordplay.
'declare' becomes 'aver' (averring is a kind of declaring).
'advancing years?' becomes 'age' (a person's age).
'aver'+'age'='AVERAGE'
'to' is the link.
(Other definitions for average that I've seen before include "Normal in arithmetic way" , "Normal; mean" , "Moderate" , "Medial" , "par" .)