How old do u have to be to open a small buisness?

Open it while you're still small. Then, when you get big, hopefully your small business will become a big business. You might need an adult cosigner, etc., but that shouldn't be a problem. There is no law that says a junior tycoon can't hire and fire adults. The big problem is money. You probably need investment capital. Junior tycoons don't usually have the credit nor the credibility to get the working capital they need for starting their businesses. But it's only because people don't trust you to have adult responsibility. If you can find a way to earn their trust, you're on your way to success.