RhymeZone: quinquagenarian definitions

Definitions of quinquagenarian:

noun: (obsolete, rare) Synonym of pentecoster: an officer who commands 50 men.
noun: Synonym of fiftysomething: a person between 50 and 59 years old.
adjective: (obsolete, rare) Of or related to command over 50 men.
adjective: Of or related to fiftysomethings.

(Definitions from Wiktionary)