Most of us who live long enough will develop osteoarthritis aka degenerative joint disease. Some will have it some up first, or almost entirely, in thumbs, some in knees, some neck, some shoulder, etc - you get the idea. Some will have it show up in their 40s and some not be bothered into their 80s.
So I think if you have no other reason than "I've done aikido a long time" and "I have been overweight a long time" you may be barking up the wrong tree (or running down a blind alley) searching for a cause. It could easily and equally have been a long forgotten minor whiplash when you were a kid or a chronic posture issue accreting over decades or something we can't identify that set up those vertebrae as the initial spot for wear and tear.
Funny thing that osteo ... I thought it was coming on in my hands last couple of years as sometimes the pain is quite severe but a recent x-ray for some thing unrelated brought out the comment from the radiologist "no signs of arthritis".