age ninety; one's nineties
Refers to the age of ninety or the decade of one's nineties. Often used in contexts like birthdays or life stages.
My grandmother is still healthy even though she has reached ninety.
We celebrated his ninetieth birthday with family.
九十代 means 'one's nineties' (the decade), but 九十路 carries a more literary or traditional nuance.
九十 (ninety) + 路 (suffix indicating an age or decade). The suffix 路 is used in words like 二十路 (age twenty) and 三十路 (age thirty), though it is less common in modern Japanese.