Politics found a loophole through the space-time continuum.
Now its on you to deal with the consequences of their actions.
(Not an official response, just making humor)

"b-but it's for the children!!"

Why we use this process

In the UK, Ofcom is the independent regulator for online safety. Ofcom’s guidance on the OSA states that one highly effective age assurance measure is credit card checks. This is because, in the UK, an individual must be at least 18 years of age to obtain a credit card, therefore credit card issuers are obliged to verify the age of an applicant before providing them with a credit card.

Having the credit card stored as a payment method acts as an additional deterrent against circumventing age verification by sharing a single Steam user account among multiple persons.

https://help.steampowered.com/en/faqs/view/292B-3DA3-CFC8-97F6

There should be a contingency regardless of government policy for accounts over 18 years old. My account is over 18 years and I don't own a credit card, and being on disability, I can't ever get one either. What this, is blatant discrimination. I shouldn't have to verify myself if my activity and existence already proves enough already... its reminds me of a time some years ago when they upped the age for alcohol when cashiers would even ask for age ID for 70-year-old pensioners just cos the gov told them to, regardless of the fact the guy looked like he was one foot into the grave. It's ridiculous.

Aaaw man, my account only has 15 "years of service". And I only created an email account, got a debit card, created this Steam account and bought my first game when I was only 2 years old. Too bad I can't prove I'm an adult, when I'm oh-so-obviously just 17.