Backing up, you would then take it that it is 1/6 at 80, 1/12 at 75, 1/24 at 70, and 1/48 at 65.And going forward, that it would be 2/3 at 90 - and 100% at 95.
Obviously, a lot of approximatin’ goin’ on . . .
In general, geometric progressions flatten out and actually approach some sort of saturation point.
The truth is closer to in the USA about 50% at 85 have some form of dementia. And if you add in any neurodegenerative disease, it’s probably more.
And the stats get screwed by the fact that many people (with or without dementia) leave the world between 80 and 85. Thus the 85 year old set contains the half of the former 80-yr-olds that had dementia, minus all the ones who died. And is added to by the healthy ones who are about 75 years old mitocondrially. Two totally different populations at 85. You really see more of an extreme in competency than at any other age.