Great! Promotion for old man (7)
I believe the answer is:
grandad
'old man' is the definition.
(elderly relative)
'great promotion' is the wordplay.
'great' becomes 'grand' (I've seen this before).
'promotion' becomes 'ad' (short for advert).
'grand'+'ad'='GRANDAD'
'for' is the link.
(Other definitions for grandad that I've seen before include "senior citizen" , "Dad rang his ancestor" , "Father's father" , "relative" , "And drag your ancestor here" .)