Seifuku no Koibito

The story starts when an elementary school boy, Chiaki, brings his classmate & friend, Masamichi, home. There the irrepressible Masamichi meets Chiaki's older brother, Tomoya. Masamichi then proceeds to call him "cute," and ask him out. There's a five-year difference between their ages, so it's understandable when Tomoya freaks. The chase begins...and continues for years, while Masa works his way through elementary school, middle school, and high school...

(Source: Translated Treasures)