User blog comment:B214/Volume 22 spoilers/@comment-201.215.165.7-20170112030400/@comment-9595671-20170112185935

True his body is made from it, but that doesn't mean Issei got that power, the bodies of Dragons have a fundamentally different physiology and even if Issei's body is Dragon his soul isn't.

While maybe due to this situation Issei may have managed to gain the same eternal youth as Dragons, until Ishibumi himself confirms it we can't think of it as true.