@DarkGura @ChristiJunior @rasterman I hate this nonsense.
People did NOT have kids at 12, at least not often, and rarely more than once (because the mother would almost certainly die).

Mortality rates, premature births, and risks of every complication under the sun skyrocket before the age of 17, and after 30.
Human biology has not changed that much in a couple hundred years.

Kids were married off young, but they didn't have sex at 12, late bloomers don't even have a sex drive at that age, many didn't have their first period.

Age at first period can change pretty drastically, mostly due to absence of a father in the house, which is why it was much higher in the more conservative society of a few decades ago.

Considering family structure, and cultural norms, average age at first period was probably higher a few centuries ago than it is now, not lower.