Is there any reason to believe that asking would be remotely reliable? There's a reason that liquor stores don't just ask people whether they're over 21.
Yet, online that’s all websites 18+ and 21+ do.
Does the liquor store estimate your age or do they ask for your id?
Google should ask and then could demand proof.
What would they ask for? You can have residency in many countries.
If they had asked the OP, he would have told them Germany, not Thailand, so they likely would not be in compliance with the law.
They could demand proof of residency, that's the correct way.