I write a lot about how Japan’s society is considered “vertical,” with concepts like senpai, a senior in a school, company or other organization, a role that comes with a degree of respect but also responsibility, such as the unwritten rule that you’ll pick up the tab at restaurants when eating with your kohai (junior) from time to time. While it’s common for a person’s “social level” to be tied to their age — an 18-year-old student in high school will be senpai to students who are younger than him — there are times when this neat social system is upset. For example, what happens if a student is held back a year, and he suddenly becomes kohai to his former classmates? (Incidentlaly, the idea of a gifted student skipping grades is totally alien in Japan.) As early as a decade ago many workers could expect to stay at the same company all their lives, but now almost no one does, which means that at some point a 35-year-old is going to change jobs and find himself working under a new senpai who’s ten years younger than he is. It’s common in anime for age-based relationships to be turned on their ears as a vehicle for more interesting characterization. For example, when Haruhi forces Mikuru to join the SOS Brigade, part of Kyon’s surprise is that Mikuru is a year older than the rest of them: so powerful is Haruhi’s personality that she bends even an older student to her will. Other examples of this tendency for age-based relationships to be skewed in anime include Tomoyo from Clannad, who speaks in a brisk, rude manner to everyone including students older than her, and Taiga from Toradora, who clashes violently with her school’s class president.
For the record, this kind of thing of thing happens in anime but not the real world very often. ^_^
It’s common in anime for characters to disregard proper age relationships.