Manga Kenja No Mago

At all times, magic has helped humanity to avoid problems and disasters. A boy named Shin, who retained memories of past lives, got to study with an old man who is called the sorcerer. He and others like him raised the boy in a cultural place, like a native. And thanks to the memories preserved from a past life, Shin easily mastered the knowledge of the Magi, and began to independently develop his own magical powers. Then the wise men told him that he should go on an independent journey at the age of 15, regretting that they had not taught him common sense. The kid, raised in special conditions, did indeed lack some common sense and communication. He travels to a distant kingdom to enroll in the local magic academy, where he must be taught witchcraft and communication.