The 8th Son? Are You Kidding Me?

Shingo Ichinomiya was a young, single salaryman when he fell asleep one night at his dinner table. When he awakens, he's at a different dinner table during a wedding ceremony and in the body of a 5-year-old boy, whom he later learns is Wendelin von Benno Baumeister. Although he initially has the impression that he's part of a well-off noble family, he soon discovers that it was all for show; his family is actually poor and illiterate and lives in a thinly-populated area on the outskirts of civilization. Further, he's the youngest of eight sons, which doesn't bode well for his prospects. However, he also discovers that he can read the local writing, which leads to him discovering that he has a rare aptitude for wind magic. When he encounters Alfred Rainford, a former court wizard who also specializes in wind magic, his prospects start looking up.

Synopsis from Anime News Network