When I was 16 I started an ISP in my bedroom. I had an 8 port octo serial cable into a computer for people to dial into, and an ISDN line going out. It's how I learned linux. Setup SMTP mailservers etc.
That's a pretty dope setup. I was running a web hosting company at that age (and likely near the same time period? late 1990s into the early 2000s). Couldn't have done the ISP thing because not even ISDN was available in my area.