Very old cardinal put on clothes (5,3)
I believe the answer is:
stone age
'very old' is the definition.
(I've seen this before)
'cardinal put on clothes' is the wordplay.
'cardinal' becomes 'one' (a cardinal number).
'put on' becomes 'stage' (to put on a show is to present or stage it).
'clothes' is an insertion indicator (some letters clothe or cover others).
'one' placed within 'stage' is 'STONE-AGE'.
(Other definitions for stone age that I've seen before include "Early period" , "Hard time" , "before copper came in" , "25 [ERA]" , "Go, senate to ancient era before metal was discovered" .)