Update two years later. Now 69 and have ridden 3,500 miles this year. Average 2014 ride 48 miles and 16.6 MPH but over 17.5 since new bike in April.

No problems with knee at all--TKR and original left one. Everyone is different however now 9 years since surgery, 6 years biking over 17,000 miles with 8,500 in past 18 months. Still getting stronger. Go for it if you will.