A prepaid card isn't a credit card. Payment processors can tell the difference between card types. You have to be 18 or older to get a credit card issued in your name (although you can add an underage authorized user to your card). And there are now other requirements needed if you're under 21 in the US, such as proof of income or a cosigner.

A prepaid card is also not a debit card (debit cards are attached to a bank account). To get a debit card you must be either 18 or have a legal guardian who is at least 18 on the account.