User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4531192-20130821185530/@comment-5593616-20130823110243

Correct me if I'm wrong, but The Mark of Athena ended on July 1st, right? So therefore Percy is still 16 in the book-verse. You can't round up people's birthdays. He still has a month and a half before his 17th birthday. Plus, if Gaea is supposed to rise on August 1st, that will most likely be the last day in HoO, which means we won't see Percy turn 17 anyway.