How old are these PJO characters?

I have tried my hardest to figure out Will’s age! I can not for the life of me figure out how old he is. So my question is: how old is Will Solace at the end of the second series? Also how old is Nico at the end of the 2nd series? I think they are either 14 and 16, 15 and 16, 15 and 17, or 16 and 17. Are any of those right?

by LionDirect7287