"Young people don't work hard, but the old people are sad" comes from the long line in Yuefu Poems. The whole poem is as follows:

Changgexing

In the green garden, sunflowers are exposed to the sun.

Spring fills the earth with hope, and everything presents a scene of prosperity.

I am always afraid that when the cold autumn comes, the trees in Ye Er will turn yellow and the grass will wither.

A hundred rivers go east to the sea, when will they return to the west?

A lazy youth, a lousy age.