Men aged badly; this is the final stage (7)
I believe the answer is:
endgame
'this is the final stage' is the definition.
(final stage of a game)
'men aged badly' is the wordplay.
'badly' indicates anagramming the letters.
'men'+'aged'='menaged'
'menaged' with letters rearranged gives 'ENDGAME'.
(Other definitions for endgame that I've seen before include "Beckett play" , "moves before mating" , "contest's final stage" , "drama" , "closing stage" .)