I am currently studying 4 AS subjects: Maths, Economics, History and Physics and although I am going over what we have done in lessons when I have spare time, I was wondering when I should put my life on hold and get down to serious revision. Any suggestions?
As soon as possible as all exams are in May-June and there are no January exams that is both good and bad. Good as you have more time and bad as you have double the exams to do. I would start after Christmas really and as you have four subjects its best to have already bagan to start now if not then during January I wouldn't leave it any longer than that personally.
At least start making notes now - especially if you have mocks in January or so. Your subjects seem to be quite heavy on knowledge and practice so try to understand what you're doing now.