Wear down when retired? (3,2)
I believe the answer is:
put on
'wear' is the definition.
(I know that wear can be written as put on)
'down when retired?' is the wordplay.
'down' becomes 'not up' (I've seen this in another clue).
'when retired?' says the letters should be written backwards (retire can mean to go back).
'notup' in reverse letter order is 'PUT-ON'.
(Other definitions for put on that I've seen before include "Apply (to a surface) - present (on stage)" , "Donned" , "Affixed" , "Don clothes or stage play" , "in an unnatural way" .)