I would be surprised if those people could be solving AP Physics C problems by 8th grade. 1 & 2, easily of course, but C is quite different.
If you found calculus BC hard-ish and physics easy in comparison, I think you were taking 1 & 2 as C was much harder. SAT II physics is a joke.
Virginia probably has some of the best STEM education in the entire country, at least the northern bit. Certainly better than what you can get at most schools outside of some in California, the boarding schools, and NYC magnets.
We had “big soviet encyclopedia” and “kid” one on our bookshelf (A point of pride for my grandparents). Nobody told me that by “kids” the authors meant “teens”, so around 13yo I devoured those books whole.
Taught me structure of the atom, chemistry and lots of fascinating physical phenomena. And made most of the physics material easy to grasp up till last HS grade.
It had little maths, concentrating more on the understanding rather than the rigorous descriptions, which made the maths to describe them quite obvious, when I had to learn them in school.
Not sure if the current state of wikipedia is better or worse for that purpose- it was much better structured and paced for sure.