Cold's terrible gripping senior citizen (7)
I believe the answer is:
oldster
'senior citizen' is the definition.
(I know that senior citizen can be written as oldster)
'cold's terrible gripping' is the wordplay.
'gripping' indicates a hidden word (the answer is held or gripped within the clue).
'OLDSTER' is hidden in the letters of 'colds terrible'.
(Other definitions for oldster that I've seen before include "One aged" , "Aged person" , "one getting on" , "Senior citizen (colloquial)" , "One no longer inexperienced" .)