User blog comment:NecrusIV/Average age of a Space Marine/@comment-1583177-20120817203428/@comment-1583177-20120817235943

Remember that time is broken in the Eye, inside the warp storm for all we know what seems like 10,000 years outside it in the Imperium, could be like 100 years for them. So simple answer, its cause they probably predate Dante, but aren't necessarily older thanks to the warp. In that case it just means that the marines still alive from the great crusade have lived a shorter amount of time than people like Dante or Ulrik.