1826 as the years of someone's life between 50 and 59; 1853 as a decade of years in a given century. See fifty.
Old English fiftig, from fif "five" (see five) + -tig "group of ten" (see -ty (1)). Cf. Old Frisian fiftich, Old Norse fimm tigir, Dutch vijftig, Old High German fimfzug, German fünfzig, Gothic fimf tigjus. U.S. colloquial fifty-fifty "in an even division" is from 1913.