I didn't get the vibe that PG was saying not to start a company in college. I may have misinterpreted him incorrectly, but to me the advice was to not do both simultaneously.
He does mention that there are certain things you can't do if you start a successful company at a young age, but to me the main point was that when you take on a startup you have to be completely invested, and if you're still in school it will be very hard to find time work on both the company and maintain your grades.
So if you exclude 20 and 21, you are still in your early twenties and you just graduated from college.
The less it costs to start a company, the less you need the permission of investors to do it. So a lot of people will be able to start companies now who never could have before.
The most interesting subset may be those in their early twenties. I'm not so excited about founders who have everything investors want except intelligence, or everything except energy. The most promising group to be liberated by the new, lower threshold are those who have everything investors want except experience." - http://www.paulgraham.com/hiring.html
If PG has genuinely changed his mind in the face of new evidence, we should award him points for that. But he should also come out and admit it.