My step-brother was a grandfather at 35, and in all likelihood he'll be a great-grandfather by 60. It's something of an historical aberration that most people t

My step-brother was a grandfather at 35, and in all likelihood he'll be a great-grandfather by 60. It's something of an historical aberration that most people today only have children within a very small window of time. Interestingly, a clear, geographically distinct trend developed in Western Europe several hundred years ago, long before the industrial revolution: https://en.wikipedia.org/wiki/Hajnal_line https://en.wikipedia.org/wiki/Hajnal_line