You can get a job when you're 15, you just can't get a job that's full-time (40 hours per week) until you're 18, and there are a whole lot more restrictions on what you work you're allowed to do, and you need parental consent. And if you get a job, you'll have to pay taxes on your earnings.
Personally, if you skip a few grades and get your high school diploma ahead of schedule, I think you should be able to work a 40-hour workweek even if you're under 18.