From Longman Dictionary of Contemporary Englishoctogenarianoc‧to‧ge‧nar‧i‧an /ˌɒktəʊdʒəˈneəriən, -tə- $ ˌɑːktoʊ-/ noun [countable] OLD/NOT YOUNGsomeone who is between 80 and 89 years old
Examples from the Corpus
octogenarian• Hiking trails combine history and nature, and are strenuous enough, or gentle enough, for both teen-agers and octogenarians.• Some 40 assemblymen are now in their nineties; almost half are octogenarians.• There were six other octogenarians also in attendance and between them they had notched up 170 years service with P&O companies.• Rumors were rampant that the octogenarian was senile and in poor health.• The octogenarians were well respected too.• Here was a man who saw modern life as a foreign country: this twinkling octogenarian came across asa time-traveller.Origin octogenarian (1800-1900) Latin octogenarius “containing eighty”, from octoginta “eighty” 