I took an IQ test in 1965 when I was in the fifth grade and scored 155. It was a school requirement
and in conjunction with an accelerated reading program known at that time as something like "SLA." I think that, in terms of sheer intelligence, I peeked in the sixth grade. In junior high school my hormones kicked in, and it's been all downhill since them
As far as I can tell, no one has yet in this three-year-old discussion has mentioned the effect that sex can have on your ability to think!!!
On a different tack --- I can't help but think that some old-time dudes like Plato and Aristotle, and Aquinas after them, had absolutely massive intellects and would max out over-the-limits on any test purporting to measure intelligence.