Late 16th century; earliest use found in Thomas Blundeville (fl. 1561), author and translator. From classical Latin sexāgēnārius that contains, or is identified in some way by, the number sixty, sixty years old, in post-classical Latin also sixtyfold (3rd cent.) from sexāgēnī sixty each (from sexāgintā sixty (from sex six + -ā- (after quadrāgintā forty) + -gintā, suffix forming cardinal numerals from thirty to ninety, related to decem ten: see decem-) + -ēnī, suffix forming distributive adjectives, after e.g. sēnī six apiece, six at a time, six) + -ārius.