[maaaats]

Where I live, you can get a bank card (not credit) as a teenager. But you are unable to put yourself in debt. So you can use the card to buy stuff, but companies should be wary of using the card details to verify future purchases.

In this case, if you pay for AdWords credit up front and then spend them, the company is fine. But if they charge a bill after the fact, the contract allowing those charges wouldn't be legal, and that's the responsibility of the professional part.