Jiisama ga Iku

While protecting his grandson from a burglar, Seitaro Asao, a tea plantation owner, gets stabbed to death. A slight mix-up by a goddess gets him, instead of his grandson, accidentally summoned to another world. Seitaro accepts to take his grandson's place and starts his new life in the new world as a man ten years younger. Things are quite eventful from the start, but the gods work in mysterious ways, and wisdom and protection from the goddess helps him overcome all obstacles.

(Source: Alpha Manga)