Neither of those points invalidate the idea presented.
Just because it's not a uniform distribution doesn't mean the average changes. Most people learning a thing earlier in life doesn't change the average rate. Even if literally every single person learned a given fact on their ninth birthday, that still averages out to the same rate.
As for your second point, you're conflating "things everyone knows" with "knowing everything". Obviously people who are 80 still don't know everything, but it's not unreasonable to assume they share a pool of common knowledge most of which was accumulated in their early life.
And even if both of those things were valid criticisms, the thing you're calling out as "inaccurate pseudoscience" is the suggestion that people shouldn't be ridiculed for not knowing things, rather we should enjoy the opportunity to share knowledge.
it's a comic and the math is a joke. the sentiment is "hey not everyone learns everything at the same time, is someone doesn't know something that seems obvious to you try to encourage them and make it fun to learn it with you instead of making fun of them for not having learned it before." no one cites this in their scientific studies as a source, i assure you.
Considering that this is an xkcd comic, I think it’s fair to suggest that most people who see this and know where it’s from will recognize that it’s mostly a joke.
The spirit of the comic is still pretty nice, though. I think that’s what really matters.
It isn't a science vs pseudoscience, it is using an easy to understand set of symbolic numbers and words that are meant to be taken together as a point. The point being that we are assholes if we don't stop to take a moment to see that we at some point were those same "10,000" and experienced shit for the first time. And that jumping on others for now being those "10,000" instead of sharing their excitement is dumb. Humans tend to like lessons and reminders that are clear to understand. We as a species have learned and taught via parables basically ever since we could speak.
Focusing on complicated but very precise data removes the whole point of the meaning being presented. Now if this were being understood to be a real study or some other situation where the numbers and science were the focus then it would very much matter. It is just a super basic lesson in social interactions presented in a nerdy way.