Korean society had been very hierarchical accoring to age until 10 years ago .
But it is not strict in these day .
Depending on each person's character, it is different a little but
basic rule is that a citizen who has a public obligation respects a fellow citizen each other regardless of age,social status, richness in public place, on official meeting, in front of audience ,at first see,online.
It is a personal choice how to speak each other in private relationship after becoming acqaintance.
Moreover, we don't consider foreigner's mistakes in conversation seriously.