Is it law to add your birthday to your Google account?

No, and it’s none of their business.

You don't have to give your REAL date of birth. Just remember what date you've given. Too many people/places having real DOB just makes identity fraud easier

You can enter 1st Jan of your birth year. Always do the same of every site you feel you need not to share your real DOB, and remember what you entered as it maybe useful when you forget your password.

Not a law. You don't have to do business with or use Google products. Google may want that info in order for you to use their products but that is a different issue.

apparently I've went a few years without it... now they are asking...

ig just make sure your google account is active...

It's a requirement set by the site, isn't it?

I never did.