What's the noun for centenarians? Here's the word you're looking for.
century
A period of 100 consecutive years; often specifically a numbered period with conventional start and end dates, e.g., the twentieth century, which stretches from (strictly) 1901 through 2000, or (informally) 1900 through 1999. The first century AD was from 1 to 100.
A unit in ancientRoman army, originally of 100 army soldiers as part of a cohort, later of more varied sizes (but typically containing 60 to 70 or 80) soldiers or other men (guards, police, firemen), commanded by a centurion.
“In the past, theaters may have opened in other places as well, and a single one was sufficient to render a people famous and memorable for an entire century.”
“If there are factors at work in the preservation of these particular texts, an increased interest in divine dreams in this particular century is not one of them.”
“At the beginning of the century the law of conservation of mass in chemical reactions was checked experimentally by Landolt and various other experimenters.”