Are heartless on stage initially for ages? (5)
I believe the answer is:
aeons
'for ages?' is the definition.
(aeon is a kind of age)
'are heartless on stage initially' is the wordplay.
'heartless' suggests removing the centre.
'initially' suggests taking the first letters.
'are' with its centre removed is 'ae'.
The initial letter of 'stage' is 's'.
'ae'+'on'+'s'='AEONS'
(Other definitions for aeons that I've seen before include "Vast ages" , "Long periods of time" .)