A long time (5)
'a long time' is the definition.
(ages can mean a very long time)
This is all the clue.
(Other definitions for ages that I've seen before include "Aeons" , "Indefinitely long time" , "Yonks" , "Epochs" , "(What seems) a very long time" .)
'a long time' is the definition.
(I know that age can be written as years)
This is all the clue.
(Other definitions for years that I've seen before include "Periods of time" , "Very long time (colloq.)" , "12 month periods" , "Measures of time" , "long period" .)
'a long time' is the definition.
(yonks can informally mean many years)
This is all the clue.
(Other definitions for yonks that I've seen before include "Ages (colloq.)" , "Donkey's years!" , "An age" , "Slangily, a long time" , "A very long time (colloq.)" .)
'a long time' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for hours that I've seen before include "A long time" , "time appointed for work" , "Matins and Vespers, say?" , "Periods of time" .)
(Other definitions for ago that I've seen before include "(Years) before the present time" , "Back (in time)" , "Earlier, gone by" , "Previously" , "Time past" .)