Mine goes back to the Gmail invite days, around 20 years ago. I’m wondering if account age alone would prove I’m now over 18. Of course, I have YouTube Premium, so they already have my credit card. I can’t imagine uploading my ID. That’s a bridge too far.
Google knows precisely who you are, if you have a cell phone and give them the number. Telcos boast about this, and sell that data for a price.
The only way to avoid this, is to buy a sim card anonymously, phone anonymously, and only pay cash to top up the minutes. The second you pay with a card for minutes, the telco links that and your ID is known.
And of course, if you use Google services on your phone, no way is your ID concealed for long.
This effort cancels out as soon as you give your mobile number to pretty much anyone. Most people have contacts stored at Google, so friends add your number with name, and Google again knows.
Google doesn't care about raw ID much, it cares about networks of people. Who you know, and who has who as contacts says a lot.
Anyhow. Point is, never give your phone number to anyone or you are never anonymous.
I don’t like this assumption, but so many things these days assume a mobile phone, and even a smartphone, that it seems hard not to have one. I need one just to login to my laptop for work. On top of that, a significant number of businesses I need to interact with have automatically opted me in to 2FA using text messaging. QR code scanning is being required more and more, even just to go out to eat.
AFAIK it is also returned when you download your Google data archive.