One of the problems after knee surgery is caused by the amount that the surgeon has to prize the joint apart to get at the inner ligaments. I know very little about the healing time of your actual problem, and you will have to take expert advice on this.
I was over twice your age when I had the lining of the femur [inner surface] removed. For some months I thought that the knee would never be stable and strong again and this had little to do with the bone surface which had been roughed up to simulate cartilage, but more to do with the working space needed.
However, after 9 months, it all started to feel a lot more stable and I took a ‘retirement-job' flying a medium weight turbo-prop with no powered rudder. Taxiing in gusty conditions was a challenge, but the work-load did nothing but good.
I would have thought that you would need about 100 to 150 lbs of pressure strength with each leg to be safe. Perhaps some of the current transport pilots will know an actual figure. [I'll ask the techies] I weighed in at around 200 lbs and finally could do one leg press-ups again*...if that's the right term.
Be careful, and take advice of the physio that is assigned by the surgeon. A knee ‘expert' once told me that lifting one's own weight over the full range on one leg, was pushing to the limits of the knee.
*Use of the rudder, will of course, NOT need the full range.
Tech link
http://www.pprune.org/forums/showthr...74#post2755674