If you're looking for anime similar to Oi-san to 40 no Monogatari, you might like these titles.
On a distant southern island, a fish (sakana) opened its mouth for a cat (neko), thus "nekozakana" (cat-fish) is born.
Zero and Shito are two cats who live in a typical neighborhood, underneath a household kotatsu. Together, the two interact with their friends such as the pink dog Hana and have other fun adventures along the way.
The story follows Shokotan, a fanatical cat lover living with 10 cats that can transform into "Miracle Cats" through magic.
The comedy story follows the daily life of a somewhat flippant Pallas's cat or manul named Manul-kun, an orange tabby cat named Chatora-kun, Sukofu-kun, and other cats.