Kilts originated in the 16th century, so they have nothing to do with the middle ages, Braveheart (except the poorly costumed movie) or vikings.
So true. As much as I love most things Scottish (being partly of Scottish descent myself), I just don't quite get the kilt thing. I'll take a pair of regular pants any day. Apparently Daggerfall had kilts (though I haven't gotten far enough in the game to see such yet), so I suppose they wouldn't be totally out of place in Skyrim. TES isn't a
direct middle ages representation anyway, just mostly.