For most people, starting too early (like now) is damaging and people quickly burn out or lose motivation. The earliest I'd recommend starting is about January, but it would be fine if you start at around March/April.
Although I did basically get perfect grades, don't leave it too late like me (I started about a week or a few days before the exams). Right now, the best thing is to at least have a solid understanding on the knowledge taught in class and by doing so, you can make the revision process more stress-free.