You might be able to have a trusted adult, probably a parent or older sibling, set up some sort of simple business entity and manage the financial aspects of things for you, and then sign the business over to your name once you come of age, but I am not 100% clear on the exact details and caveats.
Honestly, though, you're young, and unless you're in some serious trouble or live in a particularly dangerous place, you still have a few blissful years left of not having to genuinely worry about day to day financial matters, how to afford food and rent, how you're going to survive to next month. Enjoy it. It's a great time to build skills and knowledge in a low risk, low pressure environment, so that when you do get out there you have an easier time with things. But I wouldn't rush your entrepreneurial ambitions.
And yeah, there really isn't a simple way to get paid in gift cards for digital goods. Not that I know of. I mean, people could technically send codes to anyone they want by email and such, so you could maybe ask for codes as a sort of voluntary tip if they happened to like one of your games a lot, but that's honestly not likely to yield much, since people already have trouble paying for stuff if they don't have to, and adding extra steps never really helps the cause.