Getting on with a drink? Good! (5)
I believe the answer is:
aging
'getting on' is the definition.
(get on can mean to get older)
'with a drink? good' is the wordplay.
'with' is a charade indicator (letters next to each other).
'drink?' becomes 'gin' (gin is an alcoholic drink).
'good' becomes 'g' (abbreviation).
'a' put next to 'gin' is 'agin'.
'agin'+'g'='AGING'
(Other definitions for aging that I've seen before include "Maturing" , "Getting older" , "Getting old" , "development" , "Becoming more grown-up" .)