So let's say there's a causative link (see other comments here for why this may not be the case), it would take a lifetime of daily complex spatial navigation for several hours every day to significantly reduce Alzheimer's disease risk, and it's still not guaranteed. If there's a linear dose response (a big if) it would still require hours per week for decades for a more modest impact.

That seems unattainable for anyone at all.

Man, Alzheimer's disease sucks. We need more investment and more research into this horrible illness.

Personally I'm curious about the impact of super-early diagnosis, decades before symptoms, and interventions that maximally slow progress.