User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-4902593-20130521041657/@comment-3146930-20130521101836

You have to remember that the Roman Big Three is different from the Greek Big Three. We aren't even sure if Camp Jupiter has a Big Three. As far as Jason being two, this is just speculation but Juno most likely had someone raise Jason for her and had Lupa bring him to Camp Jupiter when the time was right