Setting up a business is different from state to state, county to county, and town to town. If you are serious, you'd want a lawyer and an accountant to help you, both of whom hopefully specialized in small business and intellectual property. If that seems like a lot to you, you might want to start off just keeping it a hobby until you are ready to sell, but doing that may force you to eat any expenses you normally could have claimed on your taxes.

That part is the easy part. Actually finishing a game is harder, and finding a publisher is really hard. To be honest, I have no experience with publisher part of it, but I know enough to be mostly turned off by the idea. (Though getting your game into stores without one is pretty much impossible) On top of all this, you have to find decent people to be in your company, as well as figure out what role you want to play yourself. The fact that you are worried about an age limit suggests you probably don't have the capital to hire anyone anyway.

If you are under, say, 18, I would personally either join or start a mod team or a small open source program. You want something that can be finished fast. You'll find that if you can find a group of people capable of actually putting out finished products, finding a job (or investment capital) is a lot better.

Hiring and keeping good employees is the key to successful business, which is why Google has exploded into a monster, and Microsoft hasn't released a new OS in 5 years or so. That, and managing a team of volunteers will give you the management experience you'll need to manage full-time employees.

Just keep in mind that most of my "insight" comes more form observation than experience, but I was part of a company that went from the main office being in a dining room to 6 million dollars a year in just 2 years.

Here's something to take to the bank, and believe me I know:

Always start a business with someone else's money - never your own (or your familiy's). Why? If you can't convince someone with enough capital and business sense to invest in your business, then the business plan probably isn't a good investment.

If you want to start a small business - doing handheld games or download games, you really don't need that much money - maybe $75,000 or so. This will pay for startup expenses and about 18 months of development for 1 person.

A studio that wants to do AAA console development would probably need something like $3-4 million to be fully capitalized and support 15 people for about the same amount of time.

The money will likely come from some angel investor - banks and SBA loans really HATE software companies because of the extremely high risk profile.

Once you've got the money to capitalize the business, then you can start working on finding publishing partners - which is a long hard slog, even if you have really seasoned people on your team and a really cool idea. But that's another thread altogether...