Can a credit card successfully sue someone who obtained the card at age 17, with no parental co-signer?

Yes, they can be successful.

Even though a minor cannot enter legally into a contract, once you turned 18 you made the contract legitimate by not cancelling it within a reasonable period of time.

Essentially, once you turned 18, the clock started ticking. By not cancelling the contract, you have endorsed it as an adult who is legally able to enter into the contract.

Yes, they can. Since you are now 18, and did not withdraw from the contract after turning 18, the contract is ratified and valid.

Also, you will be in major trouble if the DMV discovers that you lied about your age. So I suggest you settle this matter with the credit card company.

I think that you have to apply for a credit card. I've never heard of a company sending out cards. How would they know anything about you if you didn't apply? So, when you applied for the card you lied about your age right? You had your driver's license with the wrong date but you used that to defraud the credit card company. They SHOULD sue you and win!

They may be successful. I remember reading a case in contracts class in law school in which a minor bought a car and was later sued by the dealer for failing to make payments and the court said that even though he was a minor he was acting like an adult when he entered into the contract to buy the car and therefore could be sued like an adult.

No. Since a credit card is not alive, it can't sue anyone.

They are unlikely to succeed, but they could still ruin your credit.