An age — or some other age (3)
I believe the answer is:
era
'an age' is the definition.
(both can mean a long time)
'some other age' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ERA' can be found hidden inside 'other age'.
'or' acts as a link.
(Other definitions for era that I've seen before include "Eon" , "Age marked by a distinctive character" , "Age of importance" , "Long historic period" , "Cycle" .)