I went to school at the age of six, six years in primary school, three years in junior high school and three years in college. Going to college is about 18 years old.

A weak crown means a man is 20 years old.

In ancient times, Han men were called weak crowns at the age of 20. At this time, the hair is crowned, and the coronation ceremony is held, that is, the adult hat is put on to show adulthood, but the body is still not strong and relatively young, so it is called "weak". Crown, hat, refers to adulthood.

So after going to college, it is a year of weak crown.