And kids who access real pornography early (romance novels are harmless compared to that ...) probably have a chaotic upbringing ... I think I read somewhere that girls without stable father figures enter puberty sooner, too.

So I don't guess the hen and egg question will be solved anytime soon.

But it certainly is possible that stress (and having social contagion gender worries is stress) causes early puberty. That is a known phenomenon in plants, at least. (Well, earlier fruiting, that is, puberty isn't really a thing in plants.)

I was a fat kid, and girls who are overweight tend to hit puberty earlier... which for years had me thinking it was all my fault. There is something to body fat percentage riggering puberty but some families just tend towards earlier or later start dates. There are so many variables. But lower income tends to be associated with higher body weight, and "chaotic upbringing" is often tied to poverty... there are so, so many things. In and of itself, stress should DELAY childbearing ability - but few things in life are as cut and dried as one might hope.