Errand boys not starting for a long time (4)
I believe the answer is:
ages
'long time' is the definition.
(I've seen this before)
'errand boys not starting' is the wordplay.
'errand boys' becomes 'pages' (page is a kind of errand boy).
'not starting' means to remove the first letter.
'pages' with its initial letter removed is 'AGES'.
'for a' is the link.
(Other definitions for ages that I've seen before include "Indefinitely long time" , "Aeons" , "Yonks" , "Rock of - - (hymn)" , "Long periods" .)