Retired old man’s boring meal (6)
I believe the answer is:
repast
'meal' is the definition.
(repast can mean a meal)
'retired old man's boring' is the wordplay.
'retired' becomes 'ret' (e.g. following the name of a retired army officer).
'old man's' becomes 'pas' (both can mean someone's father).
'boring' is an insertion indicator (to bore something can mean to drill into it).
'ret' placed around 'pas' is 'REPAST'.
(Other definitions for repast that I've seen before include "A meal concerning time gone by" , "Feast, meal" , "Prates about meal" , "Banquet" , "Food - tapers (anag)" .)