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.
I downvote it to lower it in the comment rankings. Acknowledging that it is imperfect, I still like it because it gives a clue as to whether I should verify the article elsewhere. It’s not there to be the final arbiter on what truth is and I think any mod that treats it as such is woefully mistaken.