I also took the aerobic bike test they have. You put on a heart monitor and it gradually increases the load to test your heart. For a 40 years old I was in the top percentile on the graphs. It told me to get my heart rate over 138 to improve endurance and work with a load of 200 watts on the bicycle. I have to say that I am very impressed with how BJJ has allowed me to maintain a good level of fitness. Even though there are times I feel beat during sparring at the dojo and I wish I had more stamina, my heart and lungs are far stronger than they were doing P90X for 3 months then coasting for another 3 in a cycle.
I also had some older lady checking me out so obviously it was kind of creepy but that's another story.