> I'm generally okay with "how old are you?"

It's a foot in the door. Once this question exists, the next logical one is "prove it".

Ok but my phone already asks me for my name, isn't that bad too?

Same with digital IDs (for example the EU one), where you'll have to install it to provide a "zero knowledge" proof today, and since you already have everything in your phone, it'll be easy to implement the "real name" policy when registering/commenting/etc.