And I don't really know if a credit card would have worked for me since I'm not the primary person on the account
I doubt you'll have any trouble using a credit card even you're not the primary person on the account. I know a guy used his wife's credit card to pay in a supermarket, the cashier took a look at the card and then at him, didn't say anything and process the transaction
I also know a guy used his girlfriend's credit card.
Huh? I thought your birthdate and therefore your age could be hidden, if you wanted them to be
Why would a person's age be on their posts?
In your user profile, if you didn't say hide your birthday blah blah blah, your age will show up under your location in your every posts.