Grows old (4)
I believe the answer is:
ages
'grows old' is the definition.
('age' can be a synonym of 'grow old')
This is all the clue.
(Other definitions for ages that I've seen before include "Awfully long time" , "A long time (colloq.)" , "Rock of - - (hymn)" , "Historic periods or prolonged time" , "Epochs" .)