Ages upon ages of time (4)
I believe the answer is:
eons
'ages upon ages of time' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eons that I've seen before include "Long periods of time - noes have it" , "Times" , "Years and years" , "Divisions of geological time" , "Vast ages" .)