First, I'd get a second opinion. Second, I'd review how you ride, now. Are you on a road bike or one on which you are upright? Most docs I know of (and I know a few) have just the opposite thought. That you need to stay active; and that bike riding is a dynamite way of doing that. I'm 72. I started riding after I retired 5 years ago, and like most people our age, yeah, I have issues. Ortho issues. Numb hand issues when I spend too much time on the handlebar.... Kidney issues. O2 issues. And, yeah, a stroke back in February that affected my balance. Still, I'm ridin'. At our ages, issues like this go with the territory. A friend of mine went from a hybrid to a step through, because he couldn't swing his leg over the seat. But he still rides. So, get that second opinion. And think of different bikes.