It doesn’t exist, but that is what some are suggesting and hoping is going to be made with these laws being passed. It would be a really good thing for the internet and websites/apps as a whole tbh if a system like this is made, and it’s not like it would be difficult.
The sites wouldnt need your information, they would just verify that the person attempting to access the site is authenticated as being 18+.
By verifying with a central age verification system.
What has been thrown around, and what should hopefully be the solution, is that a government agency (as a last resort) or a independent trusted authority makes a system where you create an account and verify your age with your documents with them. Then they have public APIs for sites to hit - you give the site a unique key (preferably you would generate individual keys that are tied to your account for every site) and all that site does is hit that API going “Is the person that this key belongs to 18+?”, and the response is yes or no.
Simple, secure, private. The site you’re accessing doesn’t know who you are and doesn’t get your details. The age verification site also doesn’t necessarily know the site you were using, and this should not be logged either.