An Oldman in Counterworld.

An Oldman in Counterworld. manga summary: The story centers on 73-year-old Seitarō Asao, who runs a tea plantation. Due to a god's mistake, he gets transported to another world in the place of his grandchild. He then starts a second life 10 years younger as 63-year-old Seitarō. Through is wisdom of an old man and "assistance magic," he is able to live a leisurely life in his new home.