Iron and Bronze, for two (4)
I believe the answer is:
ages
'iron and bronze for two' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ages that I've seen before include "Rock of - - (hymn)" , "A long time (colloq.)" , "Historical eras" , "Sage (anag)" , "Aeons" .)