User blog comment:B214/Volume 22 spoilers/@comment-29778526-20170126060633/@comment-24941352-20170127060008

@Sky-Dragoon-Twiligth

Nope in the LN it was mentioned that the highest age a Devil can reach is 10.000 Years. First when Issei used Juggneraut Drive and decreased his lifeforce to 100 years which were 1% of the life age of a devil and the second time after the leader sealed them together away with trihexa and mendtioned maybe only Issei will see them alive again