Jouzu ni Mate ga Dekiru Kana

Overview

On his way to school, university student Minoru sees a beautiful young man standing by the window of a small Western-style building and falls in love with him at first sight. Half a year later, he is approached by Toshitsugu, the man of his dreams, and is invited into his home, where he spends the night. However, the following morning when Toshitsugu learns that Minoru is underage, he tells him he must wait until his twentieth birthday the following month.

Source: AniList