Well, the Yuramal in Colombia are the people that hold the record for the most Alzeihmer cases because many possess the gene for early onset and exhibit the diseases at 40 year of age. So for them the age is quite young. This goes to show that currently the record is held by genetic factors and not environmental factors.

But they also show that it instead of eliminating the root cause of the disease, the solution might be eliminating its symptoms instead. Cause one woman who had the gene defied all odds and exhibited the symptom of the disease in her 70s. The reasoning is that another gene she had, the Christchurch gene, protected her brain from the disease. So if someone can use that info to prevent symptoms of the disease eliminating the root cause would become secondary.

That's an egregious abuse of statistics. It seems entirely implausible that the age of dementia onset would not move in parallel with lifespan.