Getting back to the gist of this thread, I learned some Vietnamese years ago while in the military, and Vietnamese was very difficult when addressing another person. Age was most important, but not the only consideration. Rank was also important. And, nationality made a difference, also. None of that is unusual, but it was much more intricate in their society (lots of derivatives).
All the people I met early on there would address me as “Mr.”, even though I was usually younger than most of the folks I was communicating and working with. It was not what I had learned in language school, and threw me off when I first arrived there. Because of my age, I thought they would address me as “young man”, which some did once they knew me.
I had no rank, per se. I was a simple low-ranked, young serviceman. But, I learned that the Vietnamese showed respect for all western foreigners, probably since the time the Dutch were there (before the French). Who knows?
The rank thing might start with the house maid, for instance, who would almost always call the oldest to the youngest males of her boss, “Mr.” (there were exceptions, depending upon whether the parents were present or not), but not necessarily the females. They could be called either “Mrs.”, “Miss”, “girl”, “little girl”, or “baby girl”. The age of the maid would be very important in these addresses. It was all very confusing. It was something that was second nature to the Vietnamese, but very tough to learn for me.
I found that as long as I used the older “Mrs.” or “Mr.” at the start, I would not get into trouble with folks who were at least close to my age. Familiarity would sort it out in the long run, and I would be corrected as to what was proper in any particular situation. Every situation was different, depending how the Vietnamese I was associating with that day felt about me.
After 21 months there, I almost got it, but knew it would take a lot longer to become comfortable with their personal addresses. The nice part was, as people got to know me better, I became “son/friend” to them. That part I liked, and understood.