Is PG seriously implying he doesn't know where college students got the idea that they should be founding startups instead, after spending the last ten years telling them to?
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.
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.
For the record, I do recall that YC changed their policy on this rather early-on its history (explicitly advising undergrads against applying) and pg has repeatedly told "Ask HN" posters on this site not to drop out of college.
This could be partially because 10 years ago, PG thought startups were undervalued in society and wanted to preach them as a valid alternative route to success. Now startups are the new Pogs, with everybody in Intro to CS wanting to be a part of their college's official startup program. So maybe now he thinks they're overvalued and wants college kids to know that even if they could reach that "The Social Network"-ian dream (which, by definition, a majority of them can't), it wouldn't be worth it and they should enjoy their carefree life a little more before they bite off more than they can chew.
Or, like brudgers said, maybe it's a sign of personal progression. The overactive young PG wanted people to live the obsessively fast lifestyle like he did, but now the older and wiser PG thinks it wouldn't have done him too much harm if he spent a couple of more years crashing in random hotels around Beijing. Certainly the more amusing of explanations, I guess.
Not only that, but haven't the majority of the 'successful' founders in which he's invested either been in college or at least in their 20s?
Adjacent point: 99% of founders don't stick around with their companies for life like Mark Zuckerberg. That's an ideal scenario for a game-changing company. In the overwhelming majority of cases, you exit and move on.