noun
one's 50s; fifties
Refers to the age range from 50 to 59, or to people in that age group.
父は５０代で会社を辞めた。
My father quit his job in his fifties.
５０代の女性に人気の趣味は何ですか。
What hobbies are popular among women in their fifties?
Compound of 五十 (ごじゅう, 'fifty') and 代 (だい, 'generation' or 'age range').