As someone being several years over, the "old at 65" comment... I can tell you a few things. Had my ankle replaced last year after 5 years of not being able to walk without terrible pain. Knees will be replaced this fall after haying season slows down as I do nearly all the tedding and raking. I agree that taking care of the joints, and everything that you HAVE, is preferable to replacing. I have all my own teeth, a few have crowns, but I also am very adamant about filling or fixing the ones rather than replace them. HOWEVER, the joints get abused when you are young and feel that you are bullet proof, and then when you get older, that abuse/damage comes home to roost. My joint problems have all been due to accidents/injuries..... once you injure a joint, it becomes the "weakest link".....
I have tried every natural/holistic treatment imaginable, as well as some conventional stuff, before deciding on the replacements. I know they are not perfect, but I will be in a wheelchair in a year if I don't replace the knees. Pain pills do nothing except make me light headed and nauseous. I know so many that have done real well with the replacements, yes, know others that have not. Much has to do with the rehab..... and how determined you are to make it work. There are other factors, but that is the biggest thing, determination to make them work as well as possible. It also has to do with doing your homework on the surgeon and facility.... It took me all the 5 years to find the doctor that did my ankle and I am thankful that I did all that research. I have been looking at knee replacement for nearly 10 years.... and have refused to go the route that I was not fully satisfied with. Now have total faith in the doctor and the newer procedure I am going to do. Going to do this while I can still have a very good prognosis for a complete recovery and very good use in the future. I want to get back to being more active, walking and getting that sort of exercise that I cannot even attempt right now. Lose the weight that is hard to take off with the decline in physical activity that requires weight bearing on the knees.
The ankle replacement does not have quite the range of motion that I want.... aggravating, but I am still working on getting all that the mechanical joint will do. PT laughs at me sometimes.... but has said that I have more use then they expected....
SO YES, take care of what you have, but accept that there are things that can make your life much better...... if you are willing to work at it.
I expect that I will be working on the farm for at least another 20 years....as long as my mind stays with me.... I will keep the body working to keep it as healthy as possible.