働(はたら)き盛(ざか)りprime of life, prime working years

三(さん)十(じゅう)代(だい)や四(よん)十(じゅう)代(だい)は働(はたら)き盛(ざか)りである。

People in their thirties or forties are in the prime of their working life.

働(はたら)き盛(ざか)りの間(あいだ)に沢山(たくさん)お金(かね)を稼(かせ)ぐつもりです。

I plan to earn a lot of money during the prime of my working life.

私(わたし)は働(はたら)き盛(ざか)りなので、朝(あさ)から晩(ばん)まで働(はたら)いています。

Since I am in the prime of my working life, I work from morning till night.

働(はたら)き盛(ざか)りのうちにお金(かね)を蓄(たくわ)えておくに越(こ)したことはない。

There is nothing better than saving money while you are in the prime of your life.

祖父(そふ)が父(ちち)に：「働(はたら)き盛(ざか)りのうちにガンガン稼(かせ)いで富(とみ)を築(きず)きたまえ！」

My grandfather said to my father: 'Earn as much as you can while you're in the prime of your life and build your wealth!'