User blog comment:Menara/The Son of Sobek: The official PJ and Kane Chronicles Crossover/@comment-7661307-20130513160035/@comment-5885060-20130514084422

Well, I think Percy was still 16 because in the Mark of Athena, he had yet to pass his 17 birthday. And I don't think Rick counts the dates of our world in reality, but only in their world. As for Carter, I'm not exactly sure. Maybe 15, I guess.