As a beginner it is suggested to start with two classes a week, even if you are a high-end athlete already. BJJ utilizes alot of muscles that you just don’t workout when you go to the gym. How often have you heard, “Bro. I did a sick external intercostal workout today!” Regardless of your level of fitness it takes a long time for your tendons/ligaments/muscles to get used to the movements of jiu-jitsu. So best advice is to pace yourself.
After your “grappling muscles” strengthen, in a few months, you may want to train more than 2 times a week. In this case, try bumping it up to 3 times a week and see how your tendons, ligaments, joints, and muscles feel. If you don’t experience an overly increased amount of soreness, stick with the 3 times per week for a few months and then bump up to 4 times per week. A quick rule of thumb; I would recommend going only twice a week for the first 3 months. Then for the next 3 months try bumping it up to 3 times a week, and see how it goes. If everything aches drop back down to 2 times a week for a while.
When I first started I was in the worst shape of my life. I was 27 years old and nearly 200 pounds. It took 6 months before things started to feel good, and a full year before I didn’t feel as if I were about to die after every workout. Now, 13 years later I am able to train seven days a week with only the usual post workout muscle soreness experienced after any satisfying workout. The best thing I ever did for my health and wellness was get started in bjj!