Magician's Murim Adventures(2015)

At 78 years old, Midran, an archmage, has at least a solid 50 years left to live. That’s more than enough time to reach the infamous 8th circle—a place only archmages dream to go. At present, it’s a journey that requires an enormous amount of mana and has proven to be physically impossible time and time, again. But alas, that’s a problem for another day. Sleep comes first.

Then, he wakes up. Only it turns out he passed away in his slumber and has awoken in his next life as a child named Hyeon?! What the hell happened while he was asleep? And where did all his hard-earned mana go?!

(Source: Comikey)