When I was in your position last year I thought that was way too early. In fact I left it until April to start revision which was a bad choice.
My grades weren't too bad (AABd), but I don't think it was healthy or efficient, I didn't even leave my room from April onwards. So all I can say is, start early but don't burnout early on in the year, just start doing a bit every week and gradually increasing the hours you're putting in.