YouTube’s age verification system for restricted videos says that you can use a credit card to verify your identity – which are only available to people ages 18+, but then it accepts a debit card if you add one. These can are issued to people 11+ by high street banks and at age 6+ by some apps. There is therefore no point in having this verification process. How can this issue be flagged to Google staff?
That is excellent feedback, I am sure this exact situation has been worked out and accounted for by YouTube. Regardless, I would suggest you submit as feedback to the team, which you can do on any YouTube page by opening the side bar and using the Send feedback option at the bottom.