The Return of the Retired Demon Lord is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

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.