sep·tu·a·ge·nar·i·an 
(sĕp′t-ə-jə-nârē-ən, -ty-, -ch-)
(sĕp′t-ə-jə-nârē-ən, -ty-, -ch-)n.
A person who is 70 years old or between the ages of 70 and 80.
adj.
1. Being 70 years old or between the ages of 70 and 80.
2. Of or relating to a septuagenarian.
[From Latin septuāgēnārius, of the number seventy, from septuāgēnī, seventy each, from septuāgintā, seventy; see SEPTUAGINT.]