A sexagenarian is a person who is 60 to 69 years old — in their sixties. You can use it as a noun (a sexagenarian) or as an adjective (sexagenarian voters). It is a rather formal, bookish word: newspapers, doctors, and writers of life stories like it. In everyday talk, people just say someone is in their sixties, or sixty-something. Though actually, some speakers stretch it a little and use it for anyone around 60, not only the strict 60–69 window. It has nothing to do with sex (male and female). The sex- here is Latin for six, because sixty is six tens. Ordinary English has a small set of these decade-of-life words (the seventies, eighties, nineties), but sexagenarian itself stays on the formal side.

六十幾歲的人（嚴格說是 60 到 69 歲）。書面、正式；日常多半說「六十幾歲」。拉丁文 sex- 是「六」，和「性」無關。