How many teeth a horse has can tell how old it is. The meaning of the word "horse's teeth grow" is that a person grows older or older.

This is evolved from the horse teeth Tuogang or horse teeth Tuoyuan,

horse teeth Tuoyuan from "Gu Liang Zhuan-Xi Gong two years":" Xun Xi led the horse to manipulate Bibi and said: 'Bibi is still also, but the horse teeth to increase the length of the carries on.'" Later, he used the phrase "the horse's teeth are growing" to describe himself as having wasted his time and not accomplished anything.

Liu Yazi's poem "Gift to Shao Ping" reads, "The Peng Fei has not yet attempted to reach the sky, but the horse's teeth have grown longer and longer." It was also written as " Horse's Teeth Grow Longer".

Yao Xueyin, "Li Zicheng", Volume 1, Chapter 2.9: "Zhang Dajing said: 'I am honored to be associated with the general today. Dajing has been a lousy person for half a lifetime, so how can he arrogate to himself the position of a brother!

Explanation: How many teeth a horse has can tell how old it is. The metaphor is that one's years have increased in vain, but one's studies or career have not accomplished much. 徒:白白地