I would guess it's physical activity. Their diet and lifestyle are not free of all the artificial things we have like you might imagine. They even have cell pho

I would guess it's physical activity. Their diet and lifestyle are not free of all the artificial things we have like you might imagine. They even have cell phones today. But they generally have physically demanding jobs: carpentry, roofing, landscaping, farming... There are no Amish C++ devs.