Cultivating sage tales a long time (4)

I believe the answer is:

ages

I'm a little stuck... Click here to teach me more about this clue!

'long time' is the definition.
(I've seen this before)

'cultivating sage tales a' is the wordplay.
'sage' anagrams to 'AGES'.
Though, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for ages that I've seen before include "Matures" , "Indefinitely long time" , "Grows old like sage" , "Epochs" , "Yonks" .)

I've seen this clue in The Mirror.

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