I ran a 1-person company for the past 3 years (B2B SAAS). I now have 2 other partners in the company to pick up the slack and we will be hiring a few employees next month.
It's difficult to: maintain your current business (IE: new features, bug fixes, customer service) while at the same time, trying to get new business (marketing, new ideas, planning) and also have any kind of life outside the business.
You also won't be able to go on any kind of real vacation and time-off is challenging. I didn't think about these things at 20, but at 30, it's starting to become more and more important.