Agreement accepted by the old couple? (4)
I believe the answer is:
yoke
'couple?' is the definition.
('yoke' can be a synonym of 'couple')
'agreement accepted by the old' is the wordplay.
'agreement' becomes 'ok' (I've seen this in other clues).
'accepted by' means one lot of letters goes inside another.
'the old' becomes 'ye'.
'ok' put into 'ye' is 'YOKE'.
(Other definitions for yoke that I've seen before include "Enslave" , "Part of garment" , "get loaded and pull?" , "Oppressive rule" , "An oppressive and burdensome restraint" .)