My Brilliant Life (2014)

Immature and clumsy Dae-soo and beautiful but foul-mouthed Mi-ra were both seventeen-year-old teenagers when Mi-ra became pregnant.  Years later, Ah-reum is now seventeen himself, but his body is that of an eighty-year-old man. Sensing that he doesn';;t have much time left, Ah-reum writes a story about how his young parents fell in love and how he came to be, hoping to give it as a gift to them on his eighteenth birthday.