A lot of it is due to education, a difference of interest, and a little more ease when it comes to symbol manipulation [...] but little has to do with insurmountable hardware limitations.

I wonder if that makes a difference in practical terms. There's all sorts of potential in one's genes, but one has the body, brain and personal history one ends up with.

What I mean is no longer feeling like the smartest person in the room and quite definitely having to put in effort to keep up.

I haven't heard of any evidence that would suggest that there are human beings who can't understand linear algebra.

I first encountered humans who couldn't understand basic arithmetic at university, in the bit of first-year psychology where they try to bludgeon basic statistics into people's heads. People who were clearly intelligent in other regards and not failures at life, who nevertheless literally had trouble adding two numbers with a result in the thirties. I'm still boggling 25 years later, but I was there and saw it ...