Was homeschooled, which was mostly a mixture of taking university classes from 12 onward in math/science + lots of motivated self study that was evaluated solely through dinner conversation with my dad. Ended up at Stanford for grad work in applied math. My dad was a PhD in philosophy though, and I was a very self driven kid. I think it's very family dependent, and the selection bias, as others stated, of who chooses to pursue it is the biggest factor.