"As a result, my advice to anyone thinking of dropping out is to keep studying, and use every opportunity to build projects and startups on the side."
Yes. In fact, I'd go even further. Don't even try to build startups. That's premature optimization. Just build things that seem interesting. The average undergraduate hacker is more likely to discover good startup ideas that way than by making a conscious effort to work on projects that are supposed to be startups.
And unless you're Gates or Zuckerberg (protip: you're almost definitely not), that college degree is going to be infinitely more valuable to you than anything you might come up with while in college.
A lot of people think that it was because he dropped out that Zuck was so successful, but IIRC, during Startup School 2012 he said that Facebook hit 1 million users before he dropped out. So unless you're coming up with the next Facebook (and you're almost definitely not), dropping out is a boneheaded move.
Your startup can fail at any time before people give two shits about it (and most do, quite quickly), but a good degree from a quality university will stay with you for life.
In fact in many cases your resume may not even pass through the filters if you don't have college degree on it.
If you want to be a doctor or lawyer, sure. If you want to work in technology, I've never met anyone who cares. In hindsight, I believe you can optimize your path for your career which often would not include college, but admittedly it is difficult to see that path as a youth, which I suppose could make college a good default.
This is a point which often worries me, I decided to skip higher education to travel and began programming (professionally for a company) when I had just turned 19, now, 7 months in I'm starting to see that my friends who went to college and university are actually light years behind me when it comes to achievements so far.
It's a bummer that I'll probably never work for the Facebooks or Googles of the world, but there are always jobs going in tech and once you have experience, your education is pretty much irrelevant.
Your education shows your first employer that you are dedicated and know your stuff, when you go to your second job, it is your performance in job one which will instead be validated.