You do realize that (i) "zones" are just restaurants / cafes / museums that have minimum age requirements and not some demarcated city blocks where children are banned and young adults party all day and (ii) this occurs semi-frequently in the west as well.

Why should a cafe be a "no kid zone"? How do you think you'd feel as a parent ? Or if there were "No Koreans zone"?

"The West" is a rather large part of the world.