Yearn for ages (4)
I believe the answer is:
long
I believe this clue is a double definition.
'yearn' is the first definition.
(thesaurus)
'ages' is the second definition.
(thesaurus)
'for' is the link.
(Other definitions for long that I've seen before include "die" , "Thus having been treated by stretcher, perhaps" , "Yearn (for)" , "Really want" , "bought in advance" .)