> Totally, that's why I figured it's easier to just ban it for under 18s, then leave it alone for over 18s.

There is no such thing as "leave it alone for over 18s".

If you institute strict age requirements, those have to be enforced for every user account. So yes, that means every site you use would require you to go through something like a KYC process.

Privacy on the internet would be gone. You can't enforce age restrictions if you allow users to remain private.