少壮不努力，老大徒伤悲 (shào zhuàng bù nǔ lì, lǎo dà tú shāng bēi)

少壮不努力，老大徒伤悲

(shào zhuàng bù nǔ lì, lǎo dà tú shāng bēi)
English Translation: “Laziness in youth spells regret in old age.”

Meaning:
If you don’t take advantage of your youth and work hard, you will regret it. Don’t waste time.

Example:
你现在不努力工作，以后老了会后悔，少壮不努力，老大徒伤悲。
(If you don’t work hard now, you’ll regret it when you’re old—“laziness in youth spells regret in old age.”)

Source: Hello Mandarin