[Terretta]

You hit it in your first para:

It's not "age" it's current-ness.

Since most people aren't expected / empowered to learn what's next 'on the job', currentness decays, making age a stereotypical proxy for dinosaur.

Here at HN, by virtue of being here reading these comments, "this isn't you". You are making yourself aware of what's going on outside your backlog. The stereotype arises because most devs aren't here or anywhere besides chopping wood.