Couldn't have agreed more with all you! I, too, noticed that they didn't really mention the ages. This drama seems to have an element of fulfilling visual fantasies, there were quite a few scenes where I thought they evoked a real life version of 'manhua' or anime. Like when her hair was blowing in the wind, and that snow scene, just to name a few. I was wowed by how visually appealing it looked found it quite satisfying.
She's one of the first Chinese actresses that come to mind when I think of a strong female/warrior. Some other ones would be Li Xin, Bai Lu, and Liu YiFei.
Leo Wu may look a bit young, I keep saying that it's probably also due to his smaller face, but he carried his character well and looks really good in the tribal get-up and hairstyle. He comes off as this young man who had to grow up fast and shoulder more responsibilities, and suits the look of the Eagle faction. Actually, all 3 factions look their part, the bear, the wolf and the eagle. Plus Great Khan looks the part tremendously.
I do think that, ideally, the casting could have been even better, but this is pretty good for me.