> [so] that a group of people could watch the village 24/7
Matthew Walker alludes to this in his book on sleep; however, in his description it's not so much older vs younger people, it's just genetic differences that make some people sleep earlier and some later, with a fairly stable 60/40 or so distribution. Thus, the "dangerous" period (where everyone sleeps) gets reduced from 8 hours to, say, 3 hours.
I can confidently say that multiple years of waking up early as a high school student did nothing to make me a morning person. 10-15 years later I find it more difficult to sleep in to 12-1pm when given the opportunity.
As a kid, I seem to remember my grandmother always waking up obscenely early. I feel like I've watched my mother transition from a "normal" morning person who will sleep in an hour or two extra on the weekend to waking up obscenely early consistently.