User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4902593-20121115150502/@comment-3146930-20121124060728

The Fates show possible futures as there isn't one correct future. Kind of like how the Fates cut Luke's string, as he would have died anyway, but it was Percy's choice that would have resulted in Olympus being destroyed or saved. Percy growing old is one possible future.