Hierarchial Structure, or Jouge-kankei
In Japanese society, there is a strong hierarchical structure by age and grade. In any circumstances, people are expected to show respect by their language and attitude towards people who are older than or in a higher position. Japanese people are trained to behave like this since childhood, but this hierarchical structure particularly starts when they enter middle school.
Especially in middle school and high school, senpai (seniors) and kohai (juniors) relationships based on grades are very important. This hierarchical system is often called “Jouge kankei.”
During these school years, most of the students belong to a club, and if you join a sport club, this senpai-kohai relationship would be very strong and strict, and kohai should obey to senpai and treat their senpai like a king all the time. On the other hand, senpai has a role as a boss and shows the hierarchy to their kohai.
Growing up in this hierarchical environment, this Jouge kankei continues even after they enter university or they start working. The relationship would not be as strict or strong as that of middle school and high school, but people still use polite language towards their senpai.
How do Japanese people recognize this grading system and find their position in the hierarchical society? Rather than age itself, people recognize their hierarchy by the school grading system that people born from April 2nd to April 1st next year are in the same year and in the same grade.
For example, at university or in a company, people with different ages but in the same grade tend to treat each other as same-grade friends and they communicate without the hierarchical system. Therefore, when meeting for the first time, Japanese people ask each other birthdays and clarify which grade they are in. When the age difference is obvious, they do not ask their birthdays. Asking how old they are can be rude, especially for women or older people, depending on the situation.