There's very little information on your ID that Google wouldn't be able to get from other sources, except perhaps your eye color and height (targeted marketing for pants anyone?). But here's the thing, Google cares less about who you are and more about what you're interested in and looking to buy. Your drivers license number and expiration date are meaningless to them but the fact that you might want to book a trip to Sheboygan or that you've been reading reviews to find the best curling iron is gold to them. Your browsing and app usage history is way more valuable than anything on your drivers license.Do you really trust Google to delete all the id information aside from age? I don’t.
And even just the age can be used for targeted advertising or selling of user data. There’s no way to only say “I’m over 18” without handing over your exact age.