Gets older for a long time (4)
I believe the answer is:
ages
I believe this clue is a triple definition!
'gets older' is the first definition.
('age' can be a synonym of 'get older')
'for' acts as a link.
'a long' is the second definition.
(thesaurus)
'time' is the third definition.
(ages can informally mean a long period)
(Other definitions for ages that I've seen before include "Matures" , "Gets older" , "Rock of - - (hymn)" , "Sage (anag)" , "(What seems) a very long time" .)