21 years ago I was in your predicament. I was 15 years old. My two friends were 14. We were all computer geeks. I suggested we start a company catering to small businesses and individuals providing web development, computer repair and desktop publishing services.
I got us some clients here and there and they all paid us with bank checks. Even back then when banks were a little more lenient it was no mean feat to cash those checks as a minor with no bank account or even a picture ID. My home state doesn't give out ID or junior driver licenses until your 16 years old.
I also inquired about merchant accounts at the age of 15. You need one to accept a credit card. Paypal is really just a merchant account.
I went to many banks until I got to HSBC and the banker was nice enough to sit me down and really explain why I wouldn't want the responsibility of one even three years down the line when I turned 18. Long story short, a credit card user can force a charge back and your money can be clawed back 6 months after the transaction. Get too many charge backs and the bank will close your merchant account.
What I wish I knew at 15 was the concept of corporations and business agents. I didn't find out about this until I was old enough not to need it.
You go to a trusted business lawyer and have them setup a corporation on your behalf. They will also double as your registered agent. So any official legal documents would be sent to them.
Then get a second adult you trust. This person will be your project manager, sales rep, talk to the adults person. They will also be the one who opens the corporate bank account. They can also sign up for paypal, stripe or square to process credit card payments.
Yes I lost customers in high school due to our age.
Then you would be paid as either a self employed freelancer or employee, check with your accountant on what's the best way to save on taxes and how it would impact your parent's taxes.
For online websites like freelancer.com, affiliate programs, advertising accounts etc.. If they don't ask for your age and offer paypal as a payment option as far as I remember, you can open up an unverified personal paypal account and purchase $500 a month worth of things with it.
That or request payment in cryptocurrencies like ethereum. As far as I know there are no age restrictions on opening up a crypto wallet.
But most places online won't let you register because you're too young to sign a legally binding agreement.
I hope this helped. I used the three years until I became a legal adult to hone my skills and learn about business management, bookkeeping, cashflow and promotion. The biggest mistake I made as a 15 year old was not making a business lawyer my first stop.
You can also see if there's a SCORE chapter where you live. They can really help out with this kind of stuff like recommending a lawyer or accountant..