I had bilateral knee replacements two years ago, at 79. The surgeries themself were not too bad. I did not need pain meds routinely post op. Only prior to physical therapy sessions. I opted to have my surgeries done in a hospital that had a rehab unit, in the same building. I feel that is the way to go. I think I stayed there three weeks, after each surgery. There are only joint, hip surgeries there vs a rehab unit in a nursing home. I tried the nursing home route after my open heart surgery last year. I would not recommend that alternative to anyone. Signed myself out after a week and a half.
The recovery, with physical therapy, is long and painful. And it is necessary to continue the exercises after your physical therapy regimen has ended. But, it was wonderful to no longer have the hip and knee pain.
As far as long term....I am not an example. I wore my knees out, trying to compensate for numerous back problems. When I was finally able to walk normally, with the new knees, the back problems showed themselves. I no longer have pain in my knees...but, cannot walk very well due to my back.