Yes it is, paw prints. It is something of a literary term. Not one I like, either, but it is what it is at present. The differentiation does indeed primarily deal with the type world the novel is set in. Lord of The Rings, with all its lore and appendecies, is considered High Fantasy. . . Conan and the Elric of Melnibone novels are also, for all there debauchery, and moral ambiguity, considered High Fantasy. As is Dragonlance. Harry Potter is not. . . neither is The Word Void Series. But if you disagree so heartily, feel free to elucidate.
Some might define it thus, but the terms I prefer to think of things is how TVTropes defines http://tvtropes.org/pmwiki/pmwiki.php/Main/HighFantasy and http://tvtropes.org/pmwiki/pmwiki.php/Main/LowFantasy fantasy, the Elder Scrolls may carry a few elements of low fantasy, as noted on the low fantasy page, but for the most part is definately high fantasy. Magic is quite present, elves, orcs and anthropomorphic animal-like races are seen pretty often, plots often tend to deal with things like killing insane gods, finding illegitimate heirs to the throne to stop Daedric invasions, and defeating ambitious sorcerers who imprison the Emperor in another dimension and pretend to be him. Crazy fantastical weapons and artifacts are quite commonplace. On the other hand, many examples of low fantasy listed still take place in a Medieval Europe-like world. They just tend to go for a different feel from high fantasy.
The floating city is troubling. . . and sounds Like necromancers. . . everyone knows I am a fan of the Daedra. . . plus I always play as Archmage. . .
Given that the floating city is supposed to raise people as undead, I wouldn't be surprised if it is connected to necromancers, I'm not sure why they'd have a floating city, though, because it's not something I've ever associated with them in the past, hopefully, though, they'll be able to adequately explain the presence of a floating city. It needs it, since it isn't a common sight in the Elder Scrolls universe (though it doesn't sound outside the realm of possibility to me.)
As to the young ages. .. I know modern times have made us forget, but as late as a century ago, many females, possibly most, were already married and pregnant by 15 or 16. . . like Sacagewa, who was also making a name for herself with Lewis and Clark by that age. . . and many a young male had struck off on his own. So, in an archaic setting like Elder Scrolls, I hardly see it as a problem that teens are the heroes, as the notion of a Teen is really a late 19th and early twentieth century invention. Prior to about the mid eighten hundreds. . . you were either a little child, as in pre adolescent. . . or you were not, and be expected to work, keep up appearances, and depending on your gender, know your way around field, cooking fire, farm and coital bed. They did not treat teens as we do now, and as a result the teens tended to be tougher, harder and more world savvy.
While the use of young characters isn't something I would say is out of place in the world of the Elder Scrolls, I do hope it's just a storytelling choice and is not intended as a means to appeal to younger audiences. A story where the characters are, by modern standards, minors, isn't necessarily for children, but stories aimed at children or teens will often use characters below the age of 18, or at the oldest, young advlts, I certainly haven't seen too many stories aimed at teens or children with a hero above 30 years of age.