The age range from 50 to 59; someone in their fifties.
うちの父はもう５０代後半だけど、まだ元気に働いている。
My father is in his late fifties, but he's still working energetically.
５０代の消費者は品質を重視する傾向がある。
Consumers in their fifties tend to prioritize quality.
健康診断は５０代になってから頻度を上げる人が多い。
Many people increase the frequency of health checkups once they reach their fifties.