I dressed down after 50, being thus (9)
I believe the answer is:
liberated
'i dressed down after 50 being thus' is the definition.
I can't judge whether this defines the answer.
'i dressed down after 50' is the wordplay.
'dressed down' becomes 'berated' ('berate' can be a synonym of 'dress down').
'after' is a charade indicator (letters next to each other).
'50' becomes 'l' (Roman numeral).
'i'+'berated'='iberated'
'iberated' after 'l' is 'LIBERATED'.
Can you help me to learn more?
(Other definitions for liberated that I've seen before include "Free" , "Having stolen" , "Emancipated" , "Freed from social conventions" , "let loose" .)