Others eating old man’s food (6)
I believe the answer is:
repast
'food' is the definition.
(I know that repast is a type of aliment)
'others eating old man's' is the wordplay.
'others' becomes 'rest' (eg the rest of a group).
'eating' indicates putting letters inside.
'old man' becomes 'pa' (both can mean someone's father).
'rest' placed around 'pa' is 'REPAST'.
(Other definitions for repast that I've seen before include "lunch?" , "Banquet" , "A formal sort of meal" , "Food - tapers (anag)" , "Prates about meal" .)