"Being the only ice magic user in the world" <- The definition of a frog in a well.
How the heck would any of them even know that? If that world has people (or other sufficiently intelligent creatures) living in more extreme latitudes, and the planet has a climate system even remotely based on what we know of science, there will naturally be ice magic users. But then again, maybe that planet only has continents in the tropical zone and no high mountain ranges, so nobody has any experience of ice. Who knows. But it's pretty haphazard to make such an assumption. Especially Ares shouldn't assume so, since he of all people would know these facts. So, before he's sure there are no inhabited places north or south that experience winter, he actually should assume he's not the only one in the world. He might be the only one in his home country.