It's credit card OR id though. People like Experian are already offering age verification systems that check passports, driving licences etc. The government also have their own GOV.UK Verify programme which has multiple providers which prove identity and thus age.

If you can login to your government tax account, or apply for a DBS, you'll be able to prove your identity.

I don’t know if a debit card counts, because they are 16+. Many of us took a while to move onto credit cards but still had access to cashless, online and overseas payment.