@Andy Leaves 

Welcome to the forum and back to playing again.

I can't speak from experience about learning to play in advanced years though I have known hundreds, perhaps thousands through the site and shop that have done so successfully. It's probably very helpful that you played when you were younger though it could be bad as well if you feel that you should be able to contort your body the same way. LOL
I can however talk about my experiences with Yoga. I would be the person who is the least flexible of all people I know before I started doing Yoga. As a matter of a fact, I was dead against starting because my first attempts of doing Yoga when the opportunity presented itself unwillingly was a super joke. I laughed hysterically at how little I could do compared to everyone else. I literally could not stop laughing.

Today my wife and I use an app called "Down Dog" and do Yoga every day. I am many times more flexible, it's considerably less painful, and I haven't had a single backache since starting Yoga, whereas I had some severe ones prior to.

I believe that your body needs to sneak into this slowly and carefully and will adapt as long as you don't force yourself through the pain too much.

Check out our "Amazing Grace" project and consider submitting a part by Tuesday. The 5th violin part is quite simple for just about anyone.