I had a knee replacd at 47. I also worked in a rehab department for about 20 years. I am 62 now and have had no problems. The knee gets sore feeling if I walk for hours at parks or on concrete. Riding in a car for long periods of time will make it stiff feeling. I am so glad I did it. One Dr. wouldn't do it, said I was too young. I finally got a second opinion and He said I had two choices I would soon be in a wheelchair and ride all the time or have a replacement. I already knew if he would do one I was all for it because I couldn't straighten out my knee fully and couldn't bear a lot of weight on it or stand a long time so I was close to having to quit my job in rehab.
I am very glad I did it. Having worked in rehab I also have seen the other side. Some don't do well after it. I feel the biggest thing is be sure and do the exercises after surgery. It will hurt and you will feel it isn't worth it but 6 months later almost everyone says it was worth all the pain and hard work.