1) Being from 90 to 99 years old 1) Old 2) Oldster 3) Veteran 
• (n.) A person ninety years old. • (n.) A person ninety years old.
Non`a·ge·na'ri·an noun [ Latin nonagenarius containing, or consisting of, ninety, from nonageni ninety each; akin to novem nine.] A person ninety years old. 
Nonagenarian: Someone in his or her ninties, that is, between 90 and 99 years of age. See also: Age by decade.
[adj] - being from 90 to 99 years old 2. [n] - someone whose age is in the nineties
nonagenarian, nonagenary A reference to or designating the age from ninety to ninety-nine years old or one who is in his/her nineties.
adjective being from 90 to 99 years old; `the nonagenarian inhabitants of the nursing home`
of the age of 90 years, or between 90 and 100 years old.