Information adapted from Please Send Money.
Decisions involving credit cards will be yours to make as long as you are at least 18. You are free to have as many credit cards as you can obtain with a credit limit as high as you can qualify for. But being responsible for making spending decisions on your own also means being responsible for repaying the debt you've accumulated.
Credit card companies eagerly seek out college students, but remember, just because you are offered a credit card doesn't mean you have to accept it.
For more information about credit cards and managing your finances, check out Please Send Money.