Couldn't Korea also set the age limit to 21, like other countries?

Don't other countries set the age limit to under 21, even aiming for the Olympics? If Korea also looked toward the Olympics and held the Asian Games with a 21-year-old limit, wouldn't they be able to win plenty of gold medals?
Since only Korea sets it at 23, it feels a bit dull, and it seems like the only label attached to it is "solving the military service issue."