Jason is 16 or 17. He doesnt have his memory in The Lost Hero so he isnt sure. Leo and Piper are about the same age as Jason, being 16 or 17. Hazel is about 13 and Frank is around 14.
But I thought Jason was 15 or 16? What was the age difference between him and Thalia? and I reread The Son of Neptune and it says Frank was 16, unless I am mistaken. Where does it state Leo and Piper's ages?