[rossvor]

It's a convention to use roman numerals for centuries in some european countries. Parent poster probably just done it out of habit.

[puszczyk]

Thanks, I wasn’t aware it is not a “global” convention and wasn’t sure what does the parent make fun of.

One learns every day :) I will be more careful about this when writing centuries in English the next time.

Also this poster on quora have a detailed list https://www.quora.com/Why-do-we-write-century-numbers-with-I...