Always naive, never old (9)
I believe the answer is:
evergreen
'never old' is the definition.
Both the answer and definition are adjectives. Perhaps they are linked in a way I don't understand?
'always naive' is the wordplay.
'always' becomes 'ever' (synonyms).
'naive' becomes 'green' (similar in meaning).
'ever'+'green'='EVERGREEN'
Can you help me to learn more?
(Other definitions for evergreen that I've seen before include "Holly, say" , "Like Laurel" , "Having year-round foliage" , "Continually fresh" , "Not all shrubs are" .)