Wise Man’s Grandchild Kenja no Mago English Subbed

A young man is reborn in another world where he is adopted as a baby by the hero Merlin Wolford and named Shin. By his 15th birthday, Shin has accumulated all kinds of power by studying under Merlin, but one thing his adoptive grandfather didn’t give him was a lick of common sense.
(Source: Anime News Network)