Extravagant oldsters liked to be dolled up (7,2,4)
I believe the answer is:
dressed to kill
'be dolled up' is the definition.
('dressed to kill' can be a synonym of 'dolled up')
'extravagant oldsters liked' is the wordplay.
'extravagant' indicates an anagram (I've seen this in other clues).
'oldsters'+'liked'='oldstersliked'
'oldstersliked' is an anagram of 'DRESSED TO KILL'.
'to' acts as a link.
(Other definitions for dressed to kill that I've seen before include "in armour?" , "in fine threads" , "smartly attired" , "in 29 ac [BATTLEDRESS]?" , "All dolled up -- liked oldsters (anag)" .)