Several parts combine into one character.

The traditional 齡 is a phonetic-semantic compound: 齒 (tooth) + 令 (lìng, "order / command" — providing the sound). The composite reads as "what is gauged by examining teeth" = age. The etymology is wonderfully practical and survives to modern veterinary practice: ranchers and horse traders examine an animal's teeth to estimate its age. The wear pattern, the angle of incisors, the presence or absence of milk teeth — all of these tell a trained eye how old a creature is. The character preserves this folk knowledge across three thousand years. Japan simplified to 齢, Mainland China to 龄.

Korean reading "ryeong" (or "yeong" word-initially). 年齡 (yeollyeong, age — the most formal Korean term for asking someone's age), 高齡 (goryeong, advanced age), 適齡 (jeokryeong, proper age — used in gyeolhon-jeokryeonggi "marriageable age"), 老齡化 (noryeong-hwa, "aging" as demographic phenomenon — major Korean policy topic given Korea's rapid population aging), 結婚適齡期 (gyeolhon-jeokryeonggi, "marriageable age").

Mandarin líng, 2nd tone (simplified 龄). 年龄 (niánlíng, age — used widely in form-filling), 高龄 (gāolíng, advanced age), 适龄 (shìlíng, of suitable age — 适龄儿童 "school-age children"), 龄期 (língqī, age stage). The simplified form 龄 is significantly easier to write than the traditional 齡, even though the meaning is identical.

Japanese on-reading レイ (rei) — 年齢 (nenrei, age — used in formal questionnaires and statistics: 平均年齢 heikin nenrei "average age"), 高齢 (kōrei, advanced age), 適齢期 (tekireiki, "appropriate-age period" — implicitly referring to marriageable age, though increasingly contested as a social concept), 老齢 (rōrei, old age), 高齢者 (kōreisha, "advanced-age person" = senior citizen — a critical demographic and policy term given Japan's super-aged society where over 28% of population is 65+). Japan's 高齢化社会 (kōreika shakai, "aging society") and even 超高齢社会 (chōkōrei shakai, "super-aged society") are central to public discourse.

Memory aid: tooth (齒) plus 令 (sound) — measuring age by examining teeth.