How old was the ancient "late birth"?

Children, scholars, juren, Jinshi. The boy was born late in front of the scholar, the scholar was born late in front of the juren, and so on. Being an official in the same dynasty, those who entered the official position late and those who entered the official position early also claimed to be born late. Moreover, even if the boy is 60 years old and the scholar 15 years old, he should call himself a late student.