Ishigo Chidori

Troubled by his overwhelming strength, the mage too strong for the world chooses to give up on his current life and decides to be reborn a thousand years into the future. However, he is greeted by a world in which the knowledge and usage of magic have regressed drastically, leaving his ambitions of finding someone stronger than him shattered. Going by his new name Kurt, the mage encounters a girl called Lala, who encourages him to enroll at the royal capital's magic academy, easily achieved as he maintains the powers he had accumulated in his past life. Meeting new friends and foes there, the world he finds himself in has new challenges in store, but this second life may just offer the enjoyment the cheat mage Kurt desperately pursues! Source: K Manga

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. It also seems that Kurt is being looked down upon for his "Gold Magic" as it is called "Defective Magic Power" in this era. In order to investigate the mysterious decline of magic in this era, Kurt enrolled in the Magic Academy at the Royal Capital and showed his extraordinary talent where he would become unparalleled in this second life of his too!?