Your weight will be a problem. A conscientious orthopod will discuss this with you. He will ask that you lose a certain amount of weight prior to the operation. Here's where it gets "iffy". Once you reach that weight you MUST maintain it forever. The physician will chose what new joint is best and align your new knee in a specific manner. If you go back and gain the weight or even more, the joint may not be able to maintain the stability required. I have , as a medical professional, seen more than a few cases of obese , older patients who have had the replacement and had to have another due to the weight factor. I firmly believe that you should discuss this with your doctor . In any event, lifestyle changes such as maintaining correct weight , blood pressure , cholesterol etc. are not that hard to do and although you can do this at any age, the earlier the better. Once you commit to this, your replacement will be as good as new. Good luck.