Lactose intolerance is more common than lactose tolerance globally. In the unites states, something like 1 in 3 people are lactose intolerant.
It's largely genetic. Lactose tolerance can be traced to nomadic tribes that kept milk producing animals as a food source, adapting to tolerate lactose in their diet over time.
Sure, but I figured that lactose intolerance would typically manifest before the age of, say, 20. I didn't realize that people could become lactose intolerant as seniors.