Sage going out for a long time (4)
I believe the answer is:
ages
'long time' is the definition.
(I've seen this before)
'sage going out' is the wordplay.
'going out' is an anagram indicator (out can mean wrong or inaccurate).
'sage' is an anagram of 'AGES'.
'for a' acts as a link.
(Other definitions for ages that I've seen before include "Gets older" , "A long time (colloq.)" , "Indefinitely long time" , "Matures" , "(What seems) a very long time" .)