Yeah. I had thought about that, although I realized that it's probably a little more complex due to genetic isolation; that is, you've got inbreeding several generations back, even more so if your ancestors were really quite homogeneous like the Japanese. Like, instead of it being 30 mothers out, it might only be 15 or less within your region.

Does that take into account the relative lack of mixing among populations in different continents until recently?

Even assuming 20 as the average age, that makes it only 50 women per thousand years (100 ish since 1 A.D.).

And I do think 25 is a solid guess. While you could def have kids younger, you can also have them older. 25 does feel old for average age, but also, 20 feels too young for an average.

Its probs somewhere between those two, but for math, me likey round number.

So I was curious and checked what the average age for marriage was in ancient Greece, think 400 BCE. And.... 25 is old maid range. As soon as puberty kicked in they were married, as young as 14 - 16. At least if you trust Wikipedia. And since this isn't scholarly work, I mostly trust it.

Remember that not everyone is a direct line of first children. The average age of the mother of the birth of A child (contrary to her first child) seems to be around age 30 over most of history according to google.

Which does make sense if you consider that women would start getting children in their late teens (puberty used to start later) and end getting children in their 40s.

That's why for an average generation 30 years is usually taken.

Years ago I had a hospice patient that was 108 years old. Her main caregivers were her children who were in their 80's, with support of their children who were in their 50's. And yes, they had children who were also starting to have children. Family get togethers had to be something!

because of how old they must be

Usually it's because of how young the mothers were.

That's also the weird thing about the "experienced" past.

When we think about what things were like "in the past", we think of what they were like for the oldest people we know, and if we are lucky we get a couple stories from them about their parents or grandparents.

So for me, my experienced past ends in 1930.

The experienced past is the lense through which we see the whole past, even though it's such a tiny sliver of the actual past.

Remember this in this context: Whenever someone says "In the past X was always the case", what they really mean was "For my grandparents X was the case", and they likely don't even realize that.

I can tell my kids about their great-great grandparents.

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There definitely was a 0 ad, but whether that standa for anything real is another issue.

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Is there 0 bc then?