Long time (4)
'long time' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ages that I've seen before include "Donkey's years" , "Indefinitely long time" , "Times" , "Matures" , "Rock of - - (hymn)" .)
'long time' is the definition.
(eon is a kind of long time)
This is all the clue.
(Other definitions for eon that I've seen before include "Prolonged period" , "Vast age (alt. sp.)" , "Long period of time" , "plenty of time" , "Age, epoch" .)
'long time' is the definition.
(a long period of time)
This is all the clue.
(Other definitions for era that I've seen before include "Distinct period in history" , "quite some time" , "Series of years" , "Long historic period" , "Eon" .)
'long time' is the definition.
(an age is a period of time)
This is the entire clue.
(Other definitions for age that I've seen before include "Time in years" , "Grow older" , "16/18 [INDUSTRIAL REVOLUTION]" , "Plenty of time" , "Period of history" .)
(Other definitions for ago that I've seen before include "Previously" , "Earlier, gone by" , "Gone, past, since" , "Back (in time)" , "(Years) before the present time" .)