septuagenarian (adj.)

"of age 70, seventy-year-old," 1793, from Latin septuagenarius "containing seventy," from septuageni "seventy each," related to septuaginta "seventy" (see Septuagint). Noun meaning "a 70-year-old person" first recorded 1805. As an adjective, septuagenary is recorded from c. 1600.