That's not an absolute though (the race and puberty thing). I remember once reading that girls of the Hadza tribe (an ethnically African hunter-gatherer clan in Tanzania) didn't usually get their first period until 18, which actually isn't unusual in natural fertility populations
You have to keep in mind that modern hunter gatherer humans live in the fringes, that all the best and most fertile land is occupied by sedentary farming humans. This makes present day hunter gatherer humans frequently malnourished.
Also that genetically africa is by far the most diverse continent in the world (the differences between different africans groups in africa is typically greater then the differences in the multi-ethnic west) , so that two or three example groups wouldn't really tell you much about the average as a whole.
As for the different population groups mentioned, it seems consistent across multi-ethnic countries like united states, netherlands, singapore. It typically doesn't work well to compare countries due to vast condition differences. For example, Dutch consume a lot of growth hormone filled dairy, American children are 1 in 3 overweight, Koreans have a very westernized food intake (bread, cookies, fast food, sugary drinks) but still eat much more soy, fermented foods and vegetables.
The differences between groups in food intake a country like US may seem vast, but are relatively minor compared to comparing countries. Or so it seems to me as a layman.
In no society are fourteen year old girls having healthier pregnancies and are better mothers than women 20-36
It's also something that has been socially controlled for a very long time. The world with the birth control pill forgets how tightly sex is and was controlled and that the link between sex and having children has long been understood.
I think it's one of the fruits of atheism that makes people think we are and were just slaves to biological urges, that women would get pregnant simply from the age where they could.
And just because it was spread by atheists, doesn't mean it isn't widespread under christians or questionably christian people like Fuentes.