I had both done at the age of 51 on July 23, 2012. I always thought I would have it done much later, but quality of life sucked. Had them both done at the same time and my surgeon has done over 5000 surgeries, so he knows what he's doing. It wasn't fun, but I wouldn't do it any other way. One rehab and you don't have to think about going back for another one. As for when to do it? I always tell everybody that you will know when you need to do it because you look at your life and it has become defined by the condition of your knees. Think long and hard about it and do what you think is right for you. Prepare yourself mentally and physically. The hardest part for me was the inability to sleep reliably for a couple of months, but now I know it was a great decision for me. Good luck!