as well as I know, aikido will bring your body to a much better situation.
the only problem is that at the beginning, your body will start 'protesting'. you will make movements that you never did before, and sit in a way that most westerners are not used to.
however, as you may know, there are so many aikidoka over 60 and 70 years old.
many elderly aikidoka told me that aikido improved their health and especially their spine and joints.
so although some pain may disturb you at first, later it will almost surely go away and you will start to feel great.
I hope that also you will feel that aikido is for the rest of your life.
anyway you should see an expert and make sure what your knee can and can't do.
then I am sure that your sensei will take good care of you.