Nongenarian 

A ninety-something wrinkled up prune trying to give others narcissistic advice how to live to a ripe old age.

Nongenarian surpassed the stage of Octogenarian yet looking forward the next stage of Centarian.

Nongenarian by Joey Jarhead November 24, 2023

nonagenarity 

The abstract noun of nonagenarian. The act or quality of being a nonagenarian, or in their 90s.

I look forward to loving my Dad in his nonagenarity, ever agile, ever compassionate, a hero called NonaMan and an inspiration.

nonagenarity by grubecnerwal November 17, 2021