Technically, you don't need to finish high school if you get a GED. Hell, this one kid that used to piss all over school and schooling dropped out when he was 16, got his GED, and is like a year away from his masters at a state university at the age of 22. Just depends on how determined/focused you are. Does high school help? Yeah, cause when most people are 16 they aren't ready to live on their own and be their own person and what not. But it's not like dropping out of high school is the end of the world and you're doomed to work fast food chains for the rest of your life.
And even if you do, the store manager at my Steak and Shake when I used to work there pulled in like 85grand a year before bonuses, which is pretty respectable. Hell, one of the managers who was literally 20 days older than me was pulling in something like 30,000$ and had the option of running her own store when she would be 22 making something like 45,000$ a year. I'd say that's pretty substantial cash for a 22 year old to be making for working at a fast food place, wouldn't you?