Personally I want to know how they managed to get through the school system before the age of 18. The system which seems designed more to keep young people off the streets than it is to educate them.
It depends a lot on your parents. Aside from the possibility of home schooling (which has to bring about all sorts of problems for university admissions) they can do a lot to push you through more quickly, or not allow it. For one thing, they can send you to better schools that will actually look for gifted students and help them along. Alternatively, they can fight for (or against) advancement. For instance, it was twice suggested that I skip a grade, but my parents wouldn't let me because I was already small for my age and they were worried about me being picked on. Similarly, if my parents had fought for it, I could have graduated high school in 3 years. Probably could have done college in 3 years too, if I'd worked harder at it.
That said, I'm glad my parents did what they did. I'm working on my PhD in molecular biology now, and I'm in no hurry to be done. All those extra years in school didn't teach me any more bio, or math, or better writing skills, but I had a lot of fun during that time and definitely formed a lot of relationships that are important to me. That's what I always think people like this are missing out on.