If you meet a Korean at a cafe for the first time and you're at the stage of exchanging greetings and getting to know each other a little, you can ask, "How old are you, by any chance?" You might be embarrassed, but in Korea this is important for establishing the relationship. In Korean, the way you speak changes depending on the other person's age. If they're older than you, you use polite speech, and if they're about the same age or younger, you can use casual speech. So you need to know someone's age to decide what tone to use. It's not so much rude as a signal that they want to be able to talk comfortably going forward. - If someone asks your age, answer like this You can just say the number. As of 2023, Korea legally uses 'international age'. It's the age calculated from your birth date. Just saying the age calculated from the birth date on your passport is enough, so there's no need to overthink it. - When ages are similar If you're only one or two years apart, even Koreans find it awkward. In situations like this, it's fine to say first, "Just speak comfortably." If your ages are very close, people often keep using polite speech with each other, so you don't need to worry about it. - If you're a foreigner, it's fine to use only polite speech. Don’t worry if you don’t know all the rules for informal speech. It’s perfectly fine to use polite speech with everyone. It actually makes you come across as polite. Just remember that asking someone’s age isn’t rude, it’s a Korean-style consideration to figure out which speech level will be comfortable.