i don't know, i don't think theres any place you can actually check it either as no one is really keeping logs. plus a lot of the time you need to be 18 or 19 in order to sign up for certain services.
One of my first clients was a then 12 year old who set up a Pokemon site on his parents account. Sold it six years later and paid for his college education.
yeah, I started when I was 13 or 14, but it didn't turn out to be such a big website as the pokemon master made
btw. why did he sell that website, fuck college man... here I am, in my senior year working on my accounting degree and I don't have a job.