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.