Normally, I started high school on 15. According to the educational system of our country, high school is three years. He entered high school in 15. After three years of study, 18 graduated from high school and took the college entrance examination. If he is admitted, he can go to college. Of course, this is a normal situation, and it does not rule out that some individuals were not admitted in the same year after graduating from high school. After reviewing, they went to college 18, which can only be an individual phenomenon.