User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-7594114-20130402145059/@comment-5593616-20130402150539

Yes they take place in the same year, but Sea of Monsters is in June/July (Percy is 13) and Titan's Curse is in December (After August so Percy is 14). Trust me, he's 14 in TTC.