noun
one's 90s; nineties
Refers to the age range 90–99, or the decade of the 1990s depending on context. Commonly used with possessive or attributive phrases.
祖父は90代でも毎日散歩している。
My grandfather, even in his 90s, takes a walk every day.
90代の女性が一人で旅行するのは珍しい。
It's rare for a woman in her 90s to travel alone.
Compound of 九十 (ninety) and 代 (generation, era, age range).