Activity keeps your muscles toned, which helps your balance, which keeps you from falling. Yoga is really good for that also. Physical activity is just as important for your brain as mental activities for keeping your mind sharp. Try learning one new thing each day.
I use Audible.com and listen to books while I drive. A recent book was on maximizing your brain health. It said any new use of your brain activates it and makes it better.
It suggested that if you have not done crossword puzzles in a long time and you take them up, that will reinvigorate your brain. On the other hand, if your're one that does crossword puzzles as a habit, those neurons are already in place, and continuing them is not like exercise. One needs to take up a new brain activity, such as learning a new language, or start memorizing bible verses.
It was a very interesting book, "30 days to a more powerful brain" by Bruce Lewolt. My goal is not only to keep my body healthy, but to keep my mind healthy as well.
My parents are in an assisted living facility, which is more like an apartment complex, with people always available if you need help with anything. I visit there a lot and find it quite interesting, the people I now know in their 90's, they keep themselves busy and active enjoying a very good life. Then you meet others that don't really go anywhere or do anything exciting. The active people in their 90's are an inspiration to me. One guy in particular is 95 and still drives to his girlfriends house in Daytona Beech to spend the weekends doing things with her. His wife died after 60 years of marriage. But that didn't stop him, he takes college courses offered, teaches others art, (he's a painter) and is always on the run. He's still living life to the fullest, and as he says, it's a choice. One can complain about all the challenges of being old, or choose to enjoy the fact that they "got up again," have the free time, and live that day to the fullest.
Now that's a full life, active both physically and mentally.