I founded a company and had an exit while still in college full time. I had 13 employees when I was 19, I currently work for a well funded startup with top tier investors and ship code every day. Yet even with all that said I have not managed to get to the interview round.
This time around I have something a little more special in store for my application, so we shall see how this works. For me (like many others I'm sure) the problem is not selling people on the idea, it is selling qualified people on the idea. I want to bring on someone who can truly add value to the team and I want a partner not just another body.
It's just finding a way to stand out on the application process that a solo founder has a hard time with, I think many solo founders don't realize exactly how hard that is when the YC staff reads through more than 2,000 apps each cycle now.