Nishuume Cheat no Tensei Madoushi: Saikyou ga 1000-nengo ni Tensei shitara, Jinsei Yoyuu sugimashita

Having become overwhelming strong, a mage was bored with his life and decided to reincarnate in another era about 1000 years later. But after reincarnation, the mage now known as Kurt saw a world where magic had declined, and the mages of the era are overall much weaker than those of 1000 years ago.