Blurt out old demand (7)
I believe the answer is:
exclaim
'blurt out' is the definition.
(I've seen this before)
'old demand' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'demand' becomes 'claim' (claim is a kind of demand).
'ex'+'claim'='EXCLAIM'
(Other definitions for exclaim that I've seen before include "Cry out (in shock, etc)" , "Utter boldly" , "Call" , "Speak sharply" , "Blurt out" .)