That does not follow from the analysis at all.
Even today, with many more elderly surviving, 50% of the population does not show Alzheimer's symptoms.
About 10% of people over 65 have Alzheimers, about 1/3 of elderly die with some sort of dementia.
We do not know how many people had gingivitis a century or two ago. Certainly people lost teeth a lot faster. Nor do we have good information on how many had dementia a century or two a go.
Your assumption that:
The elderly would have all been institutionalized a century ago if this had any merit whatsoever.Is just an assumption.
And ignoring that the OP article is itself an assumption...
is denial. Whereas mine is a logical hypothesis. Again, got bias? Clearly.
Get your living will done; youre gonna need it.