How would you go about setting up a PC repairs and sales business at 15 years of age?

How would you go about setting up a PC repairs and sales business at 15 years of age?
Technically, you cannot own a business and conduct legal contracts- which is required if you want to own and operate a legit business- until you are 18. However, if you trust your parents or any other adults in your life, they can found the business for you and hire you as an employee. Work as an employee of their business until you are 18, then either have them transfer the business to you or buy them out. This is why you need someone you can trust: they need to recognize that you were the one with the idea and doing all the work. If they don't see that or if they see a way to exploit your efforts, then you shouldn't work for them...

Another way you can conduct business legally is to do unofficial contract work, but you shouldn't make formal guarantees of your work. Any claims you make can work against you if you make a mistake...