I, the Strongest Demon, Have Regained My Youth?! is a Manga/Manhwa/Manhua in (English/Raw) language, Comedy 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

In order to maintain his rule, Xin Sheng, the eternal demon king who ruled the world, went deep into the demon realm to find the highest and strongest power. Thousands of years later, he has become stronger and younger, and the world has also changed...