Sage cultivated for a long time (4)
I believe the answer is:
ages
'long time' is the definition.
(I've seen this in another clue)
'sage cultivated' is the wordplay.
'cultivated' indicates an anagram.
'sage' anagrammed gives 'AGES'.
'for a' is the link.
(Other definitions for ages that I've seen before include "Epochs" , "Awfully long time" , "Yonks" , "Times" , "Historic periods or prolonged time" .)