Neoro Inhae 

Se Woong became middle-aged without any proper confession to his first love. In his dried up life, Yoo Il, who is brightness and youth himself, appears. But, he is the son of his friend… and that friend of his was Se Woong’s first love. Note: - In 2021 the author re-released the series with many revisions bringing the chapter count from 24 to 29. - Includes two extra chapters.