二十歳
はたち · hatachi · JLPT N5 · noun
old
🎂 hata = old native word for twenty + chi (counter): the coming-of-age age
The kanji say twenty + years, but the reading is irregular: not nijussai but hatachi, from the native Japanese number hata (20), also heard in hatsuka (20th day). It survives because 20 was the traditional age of adulthood.
二 — two horizontal strokes 一 + 一
二 is an indicative character showing the number two with two simple horizontal lines, parallel to 一 (one) and 三 (three). The form has been stable since oracle bone script. It directly represents the concept of 'two' rather than depicting any physical object.
十 — single horizontal 一 + vertical 丨
十 originated as a simple vertical line in oracle bone script, representing the number ten, possibly from a knotted cord used for counting. Over time a horizontal stroke was added, giving the modern cross shape. It has consistently meant 'ten' or 'complete' throughout Chinese history.