User blog comment:Darkcloud1111/''The Mark of Athena'' Plot Holes/@comment-7594114-20130331070342/@comment-3285234-20130331091027

Here's the thing, you should consider WHEN IS PERCY'S BIRTHDAY.

Four of the five books happened in SUMMER. Percy's birthday is in LATE SUMMER/EARLY FALL.

So at the beginning of the series he is twelve years AND 10-11 months. He turned 13 just a few weeks after the book ends.

In sea of monsters he is 13 years and 10-11 months.

Then Titans cursed happed in late Fall/early Winter of the same year, but he is ALREADY 14 and 4 months.

Then in the begining  BotL he is STILL 14, but in the end of the book he turned 15. He had a birthday party remember?

Then in the begining of TLO he is 15, few days short of 16. THEN he turned 16.