Mark looked older, it's said (5)
I believe the answer is:
grade
'mark' is the definition.
('grade' can be a synonym of 'mark')
'looked older it's said' is the wordplay.
'looked older' becomes 'greyed'.
'it's said' shows a homophone (sound like).
'greyed' is a homophone of 'GRADE'.
(Other definitions for grade that I've seen before include "Degree" , "Rank or status" , "School mark" , "Particular level of rank, quality, etc" , "one of the entertainment moguls" .)