What? Bitcoin is perfect for porn sites because of its anonymity. If porn sites started ripping you off then they wouldn't survive for long with such a bad rep. News would quickly spread that people wernt getting what they paid for. Most sites will probably use a bitcoin payment processor too.
How will they verify your age if they adopt bitcoin as the payment system? Most legitimate sites out there won't let you get access to their stuffs without verifying that part to prevent getting their licence getting banned!
BTW, why do you worry about paying through credit card? They won't disclose your personal information
And sorry to say this but nowadays kids are smarter than you thought,they can always bypass the age verification
File sharing sites almost destroyed the porn industry. The porn sites will be more concerned about you uploading their porn to a file sharing site than checking your age. If they get you to pay by debit card and imprint your porn with a secret digital fingerprint they can sue if you upload it to a file sharing site. That's impossible for them if you pay by bitcoin and access them through a VPN.