Old lady after back massage in part of southeast Asia (5)
I believe the answer is:
burma
'part of southeast asia' is the definition.
(I know this)
'old lady after back massage' is the wordplay.
'old lady' becomes 'ma' (both can mean mother).
'after' means one lot of letters go next to another.
'back' is a reversal indicator.
'massage' becomes 'rub' (rub can mean to massage).
'rub' back-to-front is 'bur'.
'ma' after 'bur' is 'BURMA'.
'in' acts as a link.
(Other definitions for burma that I've seen before include "SE Asian country" , "It's now called Myanmar" , "Country of SE Asia" , "Country also known as Myanmar" , "Union of Myanmar" .)