Although you can start your Jiu Jitsu journey at any age, including your 40s, 50s, and 60s, it is not as simple as starting it at 18. If you are an older person starting to grapple, there are two things that you need to consider: flexibility and recovery.
BJJ is a great full-body workout. In it you activate all your muscles, from your neck on down to your calves, and heavy sparring is as good a high-intensity-interval-training session as any CrossFit class will give you.
Brazilian Jiu-jitsu can be a great form of aerobic exercise. Regular aerobic exercise can improve your health and prolong your life expectancy. It is vital to get the cardio exercise that you need in order to keep your heart healthy. Sparring is a great way to get in some exercise.