岁数 (suì shù) is a formal or neutral noun meaning 'age' — specifically, the number of years a person (or sometimes an animal or object) has lived. It literally combines 岁 (suì), meaning 'year' (especially in the context of age), and 数 (shù), meaning 'number'. Together, they form a compound noun that emphasizes the numerical aspect of age — not just 'how old someone is', but 'the count of years'. It’s commonly used in questions like '您贵姓？今年贵庚？' (What’s your surname? How old are you?) where 贵庚 is polite, and 岁数 is slightly more direct but still respectful.

Unlike 年龄 (nián líng), which is more general and widely used in both spoken and written Chinese, 岁数 carries a subtle emphasis on the exact number — for example, when verifying identity, filling out forms, or discussing eligibility requirements ('这个职位要求岁数在25到40之间'). It’s rarely used with measure words and almost never as a predicate without a verb (e.g., you wouldn’t say '他岁数很大' — instead, use '他岁数大' or better, '他年纪大').