Good after a drink to be getting on (5)
I believe the answer is:
aging
'be getting on' is the definition.
(I've seen this in another clue)
'good after a drink' is the wordplay.
'good' becomes 'g' (abbreviation).
'after' is a charade indicator (letters next to each other).
'drink' becomes 'gin' (gin is a kind of drink).
'a'+'gin'='agin'
'g' put after 'agin' is 'AGING'.
'to' is the link.
(Other definitions for aging that I've seen before include "Getting old" , "Growing older" , "Growing old in the US" , "Maturing" , "in decline" .)