As any educated Dunmer knows, all the Telvanni councilors would need vote to choose a Hortator, and the vote would have to be unanimous. It's an archaic tradition, not invoked since I was an apprentice. Since a Hortator's duty is to lead a Great House in war, and we haven't had a war in a very long time, we have no need of a Hortator.
From this I guess that Gothren was at least rather young when they appointed a Hortator the last time. One guess I had was that the war he talked about was the Imperial invasion, but then the great houses did not co-operate very well. No talk about a Hortator and the Redoran were left alone to defend the border. Any good guesses what war he could have meant? Am I just misunderstanding, so he means that the last time the council all agreed on something was back when he was an apprentice? In that case, they did perhaps agree to be neutral in that conflict so I could just have that as backup plan I guess?
Apart from that, he has been Archmagister for a long time, but not longer than Ranis Athrys is old since the previous archmagister killed her parents.
So, that's all I know. If anyone knows more, or just thinks that they know, go ahead and enlighten me