In some cultures, to pose this question to an adult you have just met, particularly someone middle-aged or older, is the height of impropriety. The question might be met with an icy stare or even outright refusal to answer.
In Vietnam, however, knowing someone’s age in relation to one’s own is essential for forming a social relationship. The Vietnamese personal pronoun system is based on family relationships as introduced in the lessons give on Wednesday, December 12, 2007 and Friday, December 14, 2007 (which discussed more about the usage of titles as second personal pronouns). While it is possible to use an impersonal form of “toi” (I) this is rarely done in everyday conversation. For example, a man will refer to his older friend as “big brother” (anh) and himself as “little brother” (em). A 60-year old woman will refer to herself as “aunt” (cô) and her 25 year old neighbor as “child” (con) or “niece” (cháu). Society is like a big family. Even those who aren’t related to each other still address each other as though they were. For this reason, even the simplest sentence, such as “I am very happy to meet you” is impossible to formulate if you haven’t figured out what your family relationship to someone would be. In this case, both the “I” and the “you” are huge, insistent question marks in the mind of the speaker, who is in fact most likely very eager not to offend. This is why asking about someone’s age often precedes the pleasantries that come first in conversations in many other cultures. (We will introduce about Vietnamese first personal pronouns for “I” and instruct you precisely how to refer yourself with those pronouns in a future lesson).
Vietnamese speakers need to know your age in order to address you in a way that is both friendly and respectful, as befits a true relative. Therefore, while learning Vietnamese language, please do not be taken aback when you find that many of your conversation in Vietnamese start with a question about your age. Likewise, you could possibly pose this question yourself to your new Vietnamese colleagues and friends if needed. You might actually find it fun to be able to ask a question that might be quite taboo in your own society!