Ask PG: Threshold of intelligence

In What We Look for in Founders, pg says that "as long as you're over a certain threshold of intelligence, what matters most is determination".

I'm almost sure (because of what I've endured in my life) that I'm determined enough to found a startup. However, even though I'm somewhat smart (as an undergrad I have way above average GPA and some nice accomplishments) I often wonder if I'm above said threshold.

Perhaps one way to find out is through your accomplishments. Still, the question "about the most impressive thing other than this startup that each founder has built or achieved" in the YC application form scares the hell out of me, when I think about what other people might have already accomplished at my age.

Should I wait until I'm better prepared before trying to start a startup? Or should I just do it now? I am the wisest man alive, for I know one thing, and that is that I know nothing. I can't help but to be overwhelmed by all the great things some people have done, and how smart they must be.

Therefore I ask pg: How do I know if I'm above that threshold of intelligence?