nonagenarian

nouns

someone whose age is in the nineties
is a type of (narrower)
an elderly person

adjectives

being from 90 to 99 years old
"the nonagenarian inhabitants of the nursing home"
is similar to
(used especially of persons) having lived for a relatively long time or attained a specific age
"his mother is very old"; "a ripe old age"; "how old are you?"