An Oldman in Counterworld is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

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.