It is fifteen years old. The language comes from the Analects of Confucius: "Confucius said:' Be determined to learn five out of ten, stand at thirty, be puzzled at forty, know the destiny at fifty, follow your ears at sixty, and follow your heart at seventy.' So later generations called 15 years old "school year". Tang Sun wrote "Book Score": "In the year of studying, pay attention to calligraphy, taste clocks, and sigh and offer rules. Zhu, a philosopher in the Southern Song Dynasty, said: "The ancients entered universities at the age of fifteen. The heart says ambition. This so-called study is also the way of university. If you are interested in it, you will never get tired of it. "It means that ancient people entered the university at the age of fifteen." "Ambition" means where the heart goes. "Learning" here refers to the way of university. The opening of "University" is "The way of university is to show virtue, to be close to the people and to stop at perfection. "The way of university" in "University" is to discover the virtues that have been ignorant in your heart, make yourself a new citizen, that is, a gentleman, and then stop when you achieve real perfection.