A father getting your old indifference (6)
I believe the answer is:
apathy
'indifference' is the definition.
(I know that indifference can be written as apathy)
'a father getting your old' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'getting' says to put letters next to each other.
'your old' becomes 'thy' ('thy' historically meant 'your').
'a'+'pa'+'thy'='APATHY'
(Other definitions for apathy that I've seen before include "Unconcern" , "lack of involvement" , "Lack of excitement" , "Flatness" , "Indifferent quality" .)