Goinkyo Maou-Sama No Kaerizaki

Goinkyo Maou-Sama No Kaerizaki summary:

A sudden bolt of lightning hits an old man...but! The lightning bolt rejuvenated him to the good-looking guy he was in his prime! His name is Gigi Allegarcia. He was called "the strongest who surpassed the strongest" and "a man who was loved by everything but magic"...he was the demon lord of the previous generation.