Anecdotally but i know a few people with adult adhd, including myself, have trouble maintaining an adequate sleep schedule. This alone may be sufficient to explain the risk of dementia
I’m of the opinion, as a sufferer and an offspring, their lack of motivation comes from undiagnosed adhd (different times).
There’s Alzheimer’s and then there’s OldTimers. The latter is a correctable condition that if prevented could, (again, my own opinion) stave off the former. The brain is a muscle, do not let it atrophy. You need to exercise all parts of it - especially social which is difficult for seniors.