Keiya Utou

Age: 26

Keiya Utou is the main male lead of the manga and anime adaptation. He works as a bodyguard for Yakuza Boss's granddaughter, a 15-year-old Isaku Senagaki for whom he develops romantic feelings, often citing that he's her father, mother, brother, friend, and lover. He lies about his age to join the same high school as Isaku in order to protect her and is known to be overprotective and sometimes said to be possessive.

(Source: Ojou to Banken-kun Wiki)