One resisting old person’s first question (7)
I believe the answer is:
opposer
'one resisting' is the definition.
(I've seen this before)
'old person's first question' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'person's first' becomes 'p' (1st letter of 'person').
'question' becomes 'poser' (poser is a kind of question).
'o'+'p'+'poser'='OPPOSER'
(Other definitions for opposer that I've seen before include "Propose to challenger" , "Person against the motion" , "Second to speak" , "Adversary" , "Second speaker in debate" .)