The story of Jii-san Baa-san Wakagaeru follows Shouzou and Ine, an elderly couple who are living a quiet life in a farming village in Aomori Prefecture. After eating a mysterious apple that they discover on their apple farm, Shozo and Ine spontaneously regain their youth, but even after being reinvigorated they continue to live life at a grandparent-ly pace. 
 
(Source: Crunchyroll News, edited)

The story is about Ine and Shouzou, two pensioners well into their 80s who are mysteriously returned to their 20s one night.
Note: Sixth place of Tsugimanga 2020 Award in the Web Manga Category
 Jiisan Baasan Wakagaeru is a web manga released on the author's pixiv and Twitter accounts, and later picked for print release by Kadokawa. 
 Includes 4 extra chapters

Kaede Saitou