I'm not sure if anyone has mentioned this yet, so I thought I would. Tavi was born the same night (or there abouts) that his father, Septimus, was killed at First Calderon. Isana, in fear of people realizing who he was, did a water crafting on him to slow his developement...this in turn caused him to look smaller/younger. She did this so that no one would associate him and Septimus when he was older and looked like him. It also caused his furies to come in late. Isana states in one of the books (I am not exactly sure which one at the moment, I think it may have been Captain's Fury after Tavi tells them who he is) that she didn't realize that it would effect his fury development.
Septimus was stationed at the Cadleron Valley for quite a while (he had to have been , he married and knocked up Isana, and then died around the time Tavi was born).
Kitai is also fifteen, as she exclaims during her and Tavi's Trial of Wits at the wax forest when he still thinks that she is a he. That was one of my all time favorite parts..."You're...your 're a GIRL!!" hahahaha. So they are pretty uch the same age, give or take a few months Im sure.
Good timeline tho! I have read the series once already and I am currently listening to it while I am at work. The second time around is even better!