Upset about advanced age (3)
I believe the answer is:
era
'age' is the definition.
(both can mean a long time)
'upset about advanced' is the wordplay.
'upset' is a reversal indicator.
'about' becomes 're' ('re' means regarding or about).
'advanced' becomes 'a' (abbreviation).
're' in reverse letter order is 'er'.
'er'+'a'='ERA'
(Other definitions for era that I've seen before include "Long historical period" , "Cycle" , "Memorable period" , "day" , "Stage" .)