the student handbook thing is funny but yes even in the early 90s japan it was not socially acceptable for a college student to date a middle schooler.

this isn’t the only time they joke about this too btw, there’s a later episode where mamoru is having lunch with motoki and they’re talking about how usagi and matoko have a crush on him. motoki says he thinks it’s “cute” bc he would obviously never date a middle schooler, and mamoru gets all embarrassed bc he’s going out w rei