1. I can't really see age in MC skins.
2. Nope
3. Yes, to me, anyway. And that skin doesn't seem "teen" to me. It has a lot of effort put into it.
4. Good lord yes.
All teen skins to me seem to feature the generic "anime" eye style (commonly originally found in Final Fantasy SNES Sprites) and real life style clothing, usually following current trends.
Bonus:
1. Nope, personally I'm not huuuuge on real life clothing skins, but I'm not gonna bias against it.
2. Yes, because it seems like they could be assembled from other skins, or put together in like Novaskin
3. Naw, it depends on the person. While I'm nowhere near being a teen, I've created both fully self-made skins, as well as some put together from other things from other skins.