Old man entering wrong country (5)
I believe the answer is:
spain
'country' is the definition.
(Spain is a country)
'old man entering wrong' is the wordplay.
'old man' becomes 'pa' (both can mean someone's father).
'entering' is an insertion indicator.
'wrong' becomes 'sin' (wrong can mean a sin or crime).
'pa' going into 'sin' is 'SPAIN'.
(Other definitions for spain that I've seen before include "Iberian country" , "EU country" , "Pains badly to be in the country" , "European monarchy" , "Catholic country" .)