MCAT involves a lot of memorization, so I wouldn’t expect to receive the same score if I take the test two years from now. However, i would be able to memorize them again and pick them up fairly quickly, since I just need to wake up my memory. Also, CARS section involves a specific type of reasoning that you’ll likely forget over time. If you have nothing better to do this summer, then it wouldn’t hurt to start reviewing concepts but don’t do any practice tests.