Nigel has already seen these comments in an earlier PM but they might be helpful for others.
I had a total knee replacement at the end of October 2019 so about 18 months in.
Some thoughts.
I went private for convenience and timing. Surgery was painless and I was out of bed and eating the same day and home the following day.
The first couple of weeks are pretty uncomfortable, quite a lot of pain, crutches, difficult to sleep and I had some constipation probably due to the pain killers.
After that recovery to normal day to day life is pretty quick and I was walking a few 100 meters, shopping, driving, going to the pub etc. by early December.
By then I was also in the Gym using the leg resistance machines, cross trainer and bike.
In January I was doing gentle hill walks, around Idwal, Aber Falls, sections of the Wales coastal path etc. and tried a bit of scrambling without problems. Also did my first post-op long haul work flight late January with no problems.
I was building on this when lockdown came along and delayed things and although I was able to do some more significant walks last summer I’m not yet climbing.
I feel that modest winter routes would probably be OK and I’m hoping to get back to gentle skiing. My main interest these days is a cruising yacht that I keep on the West Coast of Scotland, no problem with that.
Pre-op I was really struggling with day to day stuff so had to be done but I think a last resort when you’ve tried everything else. I’m 67 and a few other bits creaking as well.
A fell running friend has had both knees done (at the same time) and is pretty active, he’s in his early 80’s