Also with Deathbringer, I'm pretty sure he was only that old for the purposes of the Assassin winglet, which needed to take place before the Brightest Night for story purposes, and he needed to be old enough to be the main character of that winglet. In Book 3, he was described as a dragonet, him being 12 was only a thing later. So in my mind I'm pretending the events of Assassin happened later than they did canonically so he can be maybe a year older than her.