It means: Don't waste your time, the teenager's black hair is gray, and you can only regret it alone. "Don't wait for leisure, the boy's head is white, and he is sad" comes from Yue Fei's "Man Jiang Hong Xie Huai" in the Southern Song Dynasty. The word Yue Fei tells people to take action. Don't wait until they are old. If they want to do anything, they are powerless. Then they can only cry alone. Extended information

The whole poem "Man Jiang Hong Xie Huai":

Angry hair rushes to the crown, leaning on the railing and resting in the drizzle. Looking up, screaming at the sky, strong and fierce. Thirty fame, dust and earth, eight thousand miles of clouds and the moon. Don't be idle, white-headed, and sad.

it's not too late to be ashamed of Jing kang. When will courtiers hate it? Drive a long car and break through the lack of Helan Mountain. Hungry to eat pork, laughing and thirsty to drink Hun blood. Stay from the beginning, clean up the old mountains and rivers, and go to the sky.

The word Yue Fei inspires the patriotism of the Chinese nation. During the Anti-Japanese War, this lyric influenced the Chinese people with its deep but majestic voice.

Yue Fei (March 24th, 113—January 27th, 1142), born in Tangyin, Xiangzhou (now tangyin county, Henan), was born in Pengju. During the Southern Song Dynasty, the famous anti-Jin generals, militarists, strategists, national heroes, calligraphers and poets ranked first among the "Four Generals of Zhongxing" in the Southern Song Dynasty.