I’ve known many people, my wife included, who have had both knees replaced. Doctors tend to wait sometimes for a person to be older, as they know the plastic that replaces cartilage has a finite life expectancy of 30 years or so. I think they now have knees where they can go back in and replace that stuff. Generally, of all the people I’ve known, those who are fit in some way, actively cycling, etc…. tend to recover better and more quickly. One riding buddy had both done over a years period and was back and riding about 3 mos. after each surgery. Cycling is not an activity that stresses the joint as much as walking or running, so is a recommended activity. It’s also a somewhat painful operation, compared to hip surgery, is what I know. Depending on your pain tolerance, expect to be on some serious pain meds for a short while. Taking those speeds the healing.