Old man right for the role (4)
I believe the answer is:
part
'the role' is the definition.
(eg a part or role in a film)
'old man right' is the wordplay.
'old man' becomes 'pa' (both can mean someone's father).
'right' becomes 'rt' (abbreviation as in Rt Hon- the Right Honourable).
'pa'+'rt'='PART'
'for' is the link.
(Other definitions for part that I've seen before include "goodbye" , "Constituent - something to play?" , "Section of a whole" , "Element" , "Fraction of the whole - separate" .)