Sly age is confused with wisdom (6)
I believe the answer is:
sagely
'with wisdom' is the definition.
(synonyms)
'sly age is confused' is the wordplay.
'is confused' indicates an anagram.
'sly'+'age'='slyage'
'slyage' anagrammed gives 'SAGELY'.
(Other definitions for sagely that I've seen before include "As someone wise" , "with prudence" , "In a wise manner" , "Like wise guy" , "Wisely" .)