The age range from 40 to 49; people in their forties.
彼はもう４０代半ばで、定期健診を欠かさないようにしている。
He's already in his mid-forties and makes sure not to miss his regular checkups.
４０代になると体力の変化を感じる人が多い。
Many people notice changes in physical stamina when they reach their forties.
このアンケートは２０代と３０代、４０代以上で集計を分けています。
This survey separates results for people in their twenties, thirties, and forties and above.