Getting out of high school early doesn't make you an adult. All it makes you is a kid who doesn't have to go to school anymore. To get around that 18 age limit, you will need to be legally emancipated (made an adult in the eyes of the law).
Here is a copy of the emancipation laws for the state of California. You can become emancipated anytime after age 14.
California Family Codes Section 7120-7123
The trouble with that is, obviously, that the law expects you to already be financially independant in order to get emancipated. As you've discovered, you can't be financially independant without being emancipated. It's a helluva catch-22 situation designed, I would imagine, to prevent most kids from emancipating. Nevertheless, it's pretty much your only option.
But it's not neccesary. The problem is that you're shooting too damn high. You wanna be a Sales Associate or run your own computer repair business or whatever. What the fuck are you thinking? You don't have the experience required for anyone to put you in those positions. Sorry to say that you can't even run your own business because it requires licensing and tax forms and all that kinda bullshit that you won't be approved for.
Look, ya little dumbass, go put in a fuckin' application at McDonalds and go flip some goddamn burgers for a few years! You can't just start out in the work force with a decent damn job! Are you fucking crazy? Really, what the fuck are you thinking? You gotta start at the bottom and work your way up.
Yeah, yeah, you have five years of experience in computer repair and probably a Network+ Certification. Congratulations. Now, wanna guess how much that's worth? NOT FUCKING SHIT! Nobody in the IT industry gives a shit about about CompTIA certifications. Your years of computer repair put you on par with the about a billion other motherfuckers who know how to install, partition, and format a fucking hard drive.
I'm not trying to bust your balls here, I'm just telling you like it is. Nobody in the work force really cares that you can tell them you're able to do something. They care that you're able to show them a fucking work history to prove that you're able to do shit. Shit, I can change tires and brake pads and brake shoes and rotors, but if I go put in an application at a fucking Firestone service center, they're gonna push me right back out the fuckin' door! Why? Cuz I have no work experience in that field! Doesn't matter what I can do, it matters what I can SHOW that I can do on that fucking application.
So, there's my advice. Stop trying to skip 10 rungs on the ladder. Nobody wants to work a shit job to start out with, but that's the way it goes. My first job was working for my dad, changing spark plugs, changing tires, bleeding brake lines, etc. I hate working on cars, but that's what I had to do.
So, take a look at that first rung on the ladder and hop on. Go clean out the deep fryer, dumbass.