It's implemented by the same government body that wants more IT startups for the EU and is constantly wondering why don't people come make companies in the company.
Because you're underage and want to see porn. I've heard it's a thing that happens sometimes.
(This in reference to the stated goals of UK and various European national governments to age-gate)
If that’s what happens, you will need to use a VPN to access these sites, should you want to do that.
I would love to see EU try mass-blocking VPNs without managing to unintentionally block a bunch of AWS ranges and other accidental targets. I spin up an AWS EC2 instance, use it as a VPN, and then what is EU gonna do? Ban AWS IPs?
Sure, you can say an average person wouldn’t even really know what AWS is. So being able to spin up an AWS instance and use it as a VPN is beyond reach for for an average person. But don’t worry, there are a lot of products (some of which are nearly free) and providers addressing that exact issue.
Spoiler: EU won’t ban VPNs, unless they end up fully committed to looking like clowns that are chasing CCP ambitions, but without the CCP level of expertise and skill.
Source: I'm in the EU right now on this very path.