So sorry for the needed second TKR. I needed a new hip at age 84. I asked the doc if I was a good candidate for surgery at that age. The reply I got was that even if I were 94 and needed a new hip, I would be a candidate for surgery;. If I were 94 and needed a hip or a knee, surgery would be encouraged because it would help keep me mobile, out of a nursing home, and much more able to move than to not have the surgery.
I recovered well, it took me longer than when I was younger (I've had TKRs when I was about 65 and 70 and no problems to date w/ either).
If possible have support at home after surgery for longer than you think you'll need it. It took me about 6 weeks, my daughter left after a month and came back a few weeks later to find me almost w/o food in the refrig because I didn't have the energy or, at that point post-surgery to be sufficiently organized to make arrangements to use InstaCart or some other way to get food into the house. I was not upset about it. I managed, and loosing a few pounds didn't hurt!