‘几岁’ literally combines ‘几’ (jǐ), meaning ‘how many’ or ‘a few’, and ‘岁’ (suì), meaning ‘years old’ or ‘age’. Together, it functions as a fixed interrogative phrase meaning ‘how old’, used exclusively to ask about a person’s age in years. It is informal and commonly used in everyday speech—especially with children, friends, or acquaintances—but avoided in formal contexts like official documents or business meetings, where ‘您多大年纪？’ (nín duō dà niánjì?) is preferred.

The phrase always appears at the beginning or end of a question, often followed by ‘了’ (le) when asking about current age, or embedded in larger questions like ‘你妹妹几岁了？’ (How old is your younger sister?). It cannot be used for non-human subjects (e.g., pets or objects); for those, ‘多大’ or ‘几年了’ may be more appropriate. Tone is essential: ‘几’ must carry the third tone (jǐ), not the fourth (jì) or neutral tone.