It's never to early to start preparing for the big bad MCAT.
This is THE standardized test of your undergraduate career. It's like the SAT, only much much more important. If you're taking a class that's a med school prereq (any bio/physics/orgo).... pick up an MCAT prep manual and start going through the topics you've covered that particular subject. It will only help your course and your experience with the MCAT. You may also wish to glance through sections for courses you've already taken.
If you're in second year, you'll take it next year?? If you're already thinking about studying, why not just do some very light studying? It's a lot of material and it's never too early to know what's on the test. Even browsing the AMCAS list of MCAT topics should give you an idea about the test.
You should comfortable with this test that's coming up in the near future. Start browsing websites and pick up some study tips. Look at different med schools and see what their MCAT requirements are. Become familiar with AMCAS website and its resources, the format of the MCAT, how to register, and those details first. This has nothing to do with actual studying and it will actually save you time when you really need to study.
Set a goal for the MCAT. Prepare a timeline for the rest of your second year and the third year (which is the most crucial). Exactly when are you going to take the MCAT? Do you have clinical experience? Are you going to study over the summer for an Aug MCAT or are you going to do an internship/volunteer work of some sort? What's your courseload during the next year? I'm taking the MCAT this semester in April so my class load is relatively lighter. And from personal experience, yes I wish I had started studying earlier. Like mentioned above, 6 months is a comfortable start date. Earlier is okay too. But just start doing your research early, it will help a lot i promise 🙂