歳とし

(Toshi)

year of age (age counter).

Connection rules

＋Number + 歳 (or 才). Irregulars: 1→いっ, 8→はっ, 10→じっ/じゅっ, 20→はたち.
＋20歳 has the fully irregular traditional reading はたち — especially important because it's the age of legal adulthood in Japan.
＋For casual asking: 何歳 (なんさい); polite: おいくつ.

私わたしは20歳さいです。

Watashi wa 20 sai desu.

I am 20 years old.

「year of age (age counter)」

弟おとうとは12歳さいです。

Otouto wa 12 sai desu.

My younger brother is 12 years old.

「year of age (age counter)」