Permission to start? (2-5)
I believe the answer is:
I believe this is a double definition.
'permission' is the first definition.
(I've seen this in another clue)
'start?' is the second definition.
'to' is the link.
(Other definitions for go-ahead that I've seen before include "Pioneering (green light?)" , "Enterprisingly progressive" , "Permission to proceed" , "Enterprising" , "Up-and-coming - authorisation" .)