noun, noun which may take the genitive case particle 'no'
Refers to the period of life between young adulthood and old age, typically around 40–60. Used as a noun or with の to modify another noun.
彼はミドルエイジになってから健康に気をつけるようになった。
He started paying attention to his health after reaching middle age.
ミドルエイジの男性が増
The number of middle-aged men is increasing.