I mean, in the UK you can get a debit card from 13 years of age so I'm not sure how that helps. Credit cards no, but requiring one would exclude a massive portion of the population as they just aren't as popular.
Frankly, to me that's just an argument against requiring anything to prove your age on an online platform. It shouldn't be necessary and I consider this a bad development.
If it's 13+ that would work if the minimum age for these platforms is also 13+. It's certainly not perfect, but if implemented, it would probably not be the only way to verify your age (or it might if credit card companies are smart and pay the platforms).
Germany has similar simple ways to provide pseudo-verification, e.g. they'll use direct-deposit or direct-debit to transfer a cent or three and put a code in the subject field that you'll need to enter. It's not perfect, and they wouldn't even know who you are, since account numbers aren't tied to names, but it proves (sufficiently for them to say "we really tried") that you are the account owner. While they don't know who you are, your bank has to because of KYC, and in case of trouble they could say "talk to the bank, they know who's hiding behind this username". Of course there are edge cases and ways around it, but it's enough that they get out of hot water.
I don't really have an opinion on whether age should be verified. I'm past most minimum ages and I don't have children, so I'm not affected.
Frankly, to me that's just an argument against requiring anything to prove your age on an online platform. It shouldn't be necessary and I consider this a bad development.