Does this mean it’s valid to make fun of those who don’t know obvious things if they’re 30 or older?
No, because there are error bars on “things”, and “everyone”, and “knows”, and on “by the time they are 30”.
This means that statistically, following a Bell curve on where people land based on this, there will be some that will be much older, and much younger that have heard of a specific thing to the point of “knowing” it.
It’s literally an observation of the content of the comic. Fuck me, you people are stupid.