４０年代よんじゅうねんだい

noun

the 40s; the forties

Refers to the decade, e.g. the 1940s, or a person's age in their forties. Context determines which meaning is intended.

• 彼かれは４０年ねん代だいに生うまれた。

  He was born in the 40s.

• 父ちちはもう４０年ねん代だいだ。

  My father is already in his forties.