I'm 55 and my Father is now 80 and is now in a care home. He has Vascular Dementia, which is small strokes in the brain and can affect younger people, so its probably hard to predict who can or will get it.For your sake I very much hope so too. I've no idea of your age but you obviously have a very alert and capable mind. I have the impression that such a mind coupled with flexibility of thought militates against the incidence of dementia.
At my age i've known a number of people who've suffered dementia, and they've either been relatively inactive mentally and/or inflexible in their attitudes. Perhaps the best known example was Margaret Thatcher, who was famously inflexible and who declined into dementia quite rapidly.
.