octogenarian (n.)

"person 80 years old or 80-odd years of age," 1789, with -an + French octogénaire "aged 80," from Latin octogenarius "containing eighty," from octogeni "eighty each," related to octoginta "eighty," from octo "eight" (see eight) + -genaria "ten times," from PIE *dkm-ta-, from root *dekm- "ten." As an adjective, "eighty years of age," from 1784. An earlier adjective was octogenary (1690s).