Goddess, advanced adult around at that time (6)
I believe the answer is:
athena
'goddess' is the definition.
(I know that Athena is a goddess)
'advanced adult around at that time' is the wordplay.
'advanced' becomes 'a' (abbreviation).
'adult' becomes 'a' (abbreviation).
'around' indicates putting letters inside.
'at that time' becomes 'then' (synonyms).
'a'+'a'='aa'
'aa' placed around 'then' is 'ATHENA'.
(Other definitions for athena that I've seen before include "wise but fierce goddess" , "Greek goddess of a capital city" , "One-time goddess" , "Greek goddess of wisdom etc." .)