I've actually been doing Internet businesses starting at age 11. But my first real business was at age 16 when I started an ISP, web hosting, and shell service company over the summer. We did very well and made a nice tidy profit on that. But I began by starting and selling small websites (forums, game review sites, etc.).
I then started my second real business at 18 where we sold game server hosting, web hosting, and ventrilo services. This company lasted about a year until I took the web hosting clients, built the web hosting services up, and then sold that to a much larger NYC based web hosting company to pursue what would be lead to my third business. Note the progression in size.
My third business was a voice over IP company for computer game players called TypeFrag. I started that in 2002 during my sophomore year of college, and ran it for five years and five full-time employees all while in college until getting a buyout offer of my 50% share that I couldn't refuse during 2007 when I was 22 years old. During that time, I also launched a software company called GameComm under the TypeFrag brand. That company won first place and $75k during a business plan competition and we hired two full-time guys to build out the software for us. That's company number four.
After selling TypeFrag and GameComm, I started in on Carbonmade when I was 22 and have been working on that since. Carbonmade is company number five -- I say company when it's a registered LLC and cash positive and profitable -- and continue to work on that to this day.
So, technically, I actually have 15 years experience working on the Web, but tend to shorten that to 10, because my first "real" company (not just a small money making forum/review site, etc.) came when I was 16... 10 years ago.
You can see my bio here: http://www.crunchbase.com/person/spencer-fry