So in Germany we have an ID card with a PIN, NFC and a government app. Website owners can request to be able to use this feature. They then get a certificate from the government that has the fields they are allowed to request stored within it.
Websites can request data from the user by sending that certificate, it opens the app, it shows you the categories of data to be send, you hold your ID card to the phone, enter the PIN, and the certificate is uploaded to the ID card which verifies it. If its valid, the ID sends back the data that is specified in the certificate.
You then get presented with exactly the data that is going to be sent to the website. You can then agree or disagree. So far that is only used to log in to government websites.
This way the government does not know which sites you visit, and you only send your age to the website.
Websites can request data from the user by sending that certificate, it opens the app, it shows you the categories of data to be send, you hold your ID card to the phone, enter the PIN, and the certificate is uploaded to the ID card which verifies it. If its valid, the ID sends back the data that is specified in the certificate.
You then get presented with exactly the data that is going to be sent to the website. You can then agree or disagree. So far that is only used to log in to government websites.
This way the government does not know which sites you visit, and you only send your age to the website.