I'm 15, and I want to repair computers, which I've recently found out is considered a business even if I just do it from home? Can someone start a business when they're under 18?
Your question raises several legal issues:
Disclaimer: This information does not constitute legal advice and does not establish an attorney-client relationship.
Yes, you definitely can. Be aware of the tax implications though, and if you're organizing a business entity - check with the local law if a minor can be a member/shareholder.
You will have problems signing contracts because you are underage. You may not have a big need for this, but there will be other forms that must be filed with the government.
I would never purposefully attempt to dissuade a budding entrepreneur, but please let me insert a bit of advice. The first company I started was a residential computer service. It is a hard sell. Computers are such commodity devices. They are disposable. Why would someone pay you $250 to fix their computer when they can just replace it for $400-450? The work you do get, half the people will not pay. You have to market far and wide to get enough work to make it worthwhile.
If you have 20-30 people that come to you for computer advice and such, if you start charging for it that number will drop to almost zero. The sad thing with residential computer service is that everyone has a teenager like you that will do the work for free or nearly so. Consumers are cheap. Not to mention that, of the work I did get, lots of the checks I was paid with bounced. You will remove malware and then the next day they will do what you told them not to and go where you advised them not to, it will be back and then they will expect you to come back and fix it for free.
I am not saying to not do it, and I am not saying that it cannot be done. It is just an uphill battle. Be prepared. The way that Geek Squad succeeds is that they can piggyback off of the Best Buy name, both in marketing and overhead.
Call your local city hall and ask to talk with someone who knows about business licensing. Ask them about age requirements for a license to do business in your city.
I suspect you'll need your parents involved since, as a minor, they are legally responsible for you and your actions. Good luck!