If you are not 18 yet and want to get a credit card could you get a guardian to cosign?

No, this is not possible. Legally, you have to enter a binding contract with a credit company, and even with a cosigner, no one under the age of 18 can legally enter into a contract. If you are emancipated, then you are considered a legal adult, and then that would be a different story. Other than that, this is not possible. -Jesse