The Adventure of the Boy With a Mind of a Middle-aged Man

★Gray Milard was born as the third son of the Milard family, the poorest noble family in the empire. In the Milard domain, his wicked stepmother had turned his biological father, the lord of the domain, into a puppet and was ruling with an iron fist. 　Gray, who dislikes trouble, decides to leave the domain immediately. Ignoring the suffering of the domain's people, he resolves to devote himself solely to self-improvement until he turns thirteen, when his parents' guardianship expires... This is the story of a young boy with the body of a child but the mind of an old man, embarking on a journey of self-improvement. (From 身体は児童、中身はおっさんの成り上がり冒険記's syosetu page.)