The department of Social security could have created some sort of public/private key pair to very age and DOB. But that's too much to ask for isn't it?

so instead of creating some kind of authorization system that would not require sending your private information to everyone the govt did nothing and instead put that responsibility on EVERY company. begs the question why rushing so much?

I would suppose that this is because there is not a single way valid for every govt. For example, in Italy we have SPID, which is different from what Germany, France and every EU state have.
If Discord wanted to use it, they had to implement a numbers of way to do it, which can be not that easy.