Dunno, if I was a wizard just returning from a 50 years nap, I'd party like crazy, instead of giving up my life for a dude just met.
It was mentioned that he actually travelled through time in that 50 years. He said he lived on a different time. He also mentioned that when Jay ever meet him in the future, he said to forgive him if they meet because he still doesn't know him at that time. So maybe he knows stuff and actually came from the future, where Jay played a role or something. Maybe that's why he readily gave Jay the precious stone. (●'◡'●)ノ
Did something happen to the artist? Around chapter 21 the art got weird.