Seek a second opinion. That doctor is not listening to you. Something other than aging is going on and it should be properly investigated.
edit: is severe arthritis in your family (or any other bone/joint disease)? Are you exposed to large or long term doses of chemical(s) or radiation in your life through work or living environment (industrial zone nearby/upwind, or very old home). These are things I’d be considering.
My condolences for your loss.