They are usually meaningful within a given company and become increasingly important as the company grows in size. Comparing titles between companies is usually pointless.
This is the tongue-in-cheek point that the post you're replying to is making. :)
Perhaps so, but I have seen innumerable posts here that do take the concept of "being senior" seriously.
Go up a few paragraphs to where the author first uses "senior" and the narrative thread to that phrase ("senior at 22") makes a lot more sense.
I think that is the point the original author is making yes