Koreans call everyone uncles and aunties. How big is Korean family?
Following is a reproduction of a related article, at my best knowledge plus/minus details.
At times, Koreans use family or relatives titles when addressing someone they don't know. First time I was in Korea, I heard many people saying auntie, uncle, grandmother and grandfather each other, leaving me wondering how many relatives they had. As I grew up there, I learned those titles can be used between strangers, which answered my question.
Two of the most commonly used titles are 아저씨 (uncle) and 아주머니 (auntie). Some times 아줌마 is used instead of 아주머니. 아주머니 sounds more formal and polite whereas 아줌마 sounds casual and may come across as being rude.
Originally 아저씨 and 아주머니 were used amongst family members. People also use the title 아주머니 to address a married woman, and, 아저씨 a man; and generally speaking, in their thirties to early sixties. A woman or a man who has grandchildren are addressed as 할머니 (grandmother) or 할아버지 (grandfather). Only until about 20 years ago, people in their late sixties were usually addressed with these titles. But these days, 할아버지 and 할머니 titles are not used unless their physical appearances show clear signs as seniors who would be having grandchildren.
Overall, there is no clear distinguished age limits for these titles. People choose the title roughly by the person's appearance, which can be impolite. For example, it is very impolite to call a young lady 아주머니. It may offend a woman if you call her 할머니. So if in doubt, it's better to choose a title for younger. When I go to a restaurant and want more side dishes, I tend to call waitresses 아가씨 (young lady). It surely make them happy.
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