年纪 (niánjì) literally combines 年 (nián, 'year') and 纪 (jì, 'era' or 'period'), together meaning 'age'—specifically a person's chronological age in years. It is a neutral, standard noun used in both spoken and written Chinese, commonly appearing in questions like '你多大年纪？' ('How old are you?') and statements about life stages, such as youth, middle age, or old age.

Unlike the more formal term 年龄 (niánlíng), which is preferred in official documents or medical contexts, 年纪 carries a slightly more conversational, human-centered tone—it often implies social or experiential implications of age (e.g., suitability for a role, maturity level, or generational perspective). It’s frequently used with modifiers like 大 (dà, 'advanced'), 小 (xiǎo, 'young'), or 轻 (qīng, 'young') to describe relative age status, especially in comparisons or judgments about appropriateness.