Deletion of age certain (7)
I believe the answer is:
erasure
'deletion' is the definition.
(I know that erasure is a type of deletion)
'age certain' is the wordplay.
'age' becomes 'era' (both can mean a long time).
'certain' becomes 'sure' (synonyms).
'era'+'sure'='ERASURE'
'of' is the link.
(Other definitions for erasure that I've seen before include "group from the 80s" , "clearing of tape" , "Deletion by an act of expunging" , "Removal" , "Effect of surface damage" .)