When I had my original accident, I was in hospital for about three weeks, during that time quite a few very elderly ladies came in with broken hips, one in the bed next to me was 94. The doctors gave her a hip replacement without any seeming worries, and she was fine.
Orthodoc, you will know far more about this than I do, but with modern anaesthetics age doesn't seem to be a big factor.
Is it easier to replace a hip, or are knees replaced on people of this age successfully as well on a regular basis?