盛年不重来，一日难再晨。

及时当勉励，岁月不待人。

晋·陶渊明《杂诗》十二首之一

The exuberant years of life will not return,

The morning of the day does not repeat itself.

Seize your time and brace yourself up,

For time does not stop to wait for you.

Tao Yuanming (365-427), poet of the Jin Dynasty

青春须早为，岂能长少年！

唐·孟郊《劝学》

Do something worthy while you are young, for youth does not stay long.

Meng Jiao (751-814), poet of the Tang Dynasty

少则志一而难忘，长则神放而易失。

《抱朴子·勖学》

As a child's mind is focused, he is not apt to forget what he learns; as an adult's mind is divided, what he has learned easily escapes his memory.

Baopuzi by Ge Hong (284-364) of the East Jin Dynasty

生也有涯，而知也无涯。

《庄子·养生主》

Life is finite, but knowledge is infinite.

Zhuangzi by Zhuang Zhou (c. 369-286 BC) and his followers of the Warring States Period

圣人不贵尺之璧而重寸之阴，时难得而易失也。

《淮南子·原道训》

A sage cherishes an inch of time instead of a foot of jade, because time is hard to attain and easy to lose.

Huainanzi by Prince Huainan Liu An (179-122 BC) and some of his followers of the Western Han Dynasty

子在川上曰：“逝者如斯夫，不舍昼夜。”

《论语·子罕》

The Master, standing by the river, said, “Time passes by like this, flowing away day and night.”

The Analects, A Confucian classic recording the words and deeds of Confucius and his dialogues with his disciples

去者日以疏，来者日以亲。

汉·无名氏《古诗十九首》之十四

The days gone by are fading further and further away, and old age is getting nearer day by day.

Collection of 19 Poems by anonymous poet(s) of the Han Dynasty

人生天地之间，若白驹之过郤，忽然而已。

《庄子·知北游》

The existence of man between heaven and earth is like a white colt bolting past a chink.

Zhuangzi by Zhuang Zhou (369-286 BC) and his followers of the Warring States Period

少年安得长少年，海波尚变为桑田。

唐·李贺《嘲少年》

How can the young stay young for good,

Even oceans can become cropland.

Li He (790-846), poet of the Tang Dynasty

百川东到海，何时复西归？

少壮不努力，老大徒伤悲。

汉·无名氏《长歌行》

All rivers flow into the East Sea.

They never flow back to the west.

If you do not work hard when young,

It's no use crying over spilt milk when old.

An anonymous poet of the Han Dynasty