To be uncharitable, you are taking an unreasonably narrow view because you disagree with Eich (I do too), but like with freedom of speech it's all about the case when you do disagree.
In this context, someone was implying that discriminating against someone based on their age is the same as discriminating against them based on their political or religious views. It's a false equivalence, because you choose your political and religious beliefs, you don't choose your age.
I'm not arguing for or against discrimination; it's a complicated topic. I just felt like in this context, parent was using a false equivalence to discredit identity politics, and I took the opportunity to try and speak out about the difference between ascribed and achieved statuses. I do disagree with Eich, but I think that's immaterial.