sexagenarian UK /ˌsɛksəd͡ʒɪˈnɛəɹɪən/US /ˌsɛksəd͡ʒɪˈnɛɹiən/adjective 1noun 1forms 1 adjective1 •Of or related to sixtysomethings. noun1 •Synonym of sixtysomething: a person between 60 and 69 years old.Luxury hotels and travel planners must be licking their lips at the prospect that a significant portion of those new sexagenarians will want the trip of a lifetime (and hang the kids' inheritance…). — 2010 formssexagenarians