You guys even sure the Wiz would trade Gil for KG, even if it were straight up? Age does mean a lot jrt, when you're trying to build for the future. Let's just say the Wiz trade Arenas to the Wolves for KG straight up. Does that get KG any closer to the contender status that he wants. Hell no. The Wiz would still be a 4/5 seed at best, and they wouldn't be able to get past a team like Miami and Detroit.
Meanwhile, the Wolves would get a franchise player who's only 25. Five years less than KG. I'm not saying the Wolves would be any closer to contention either with Gil, but chances are, they would have a franchise guy for five years longer than the Wolves would if that 1 for 1 deal went down.
The point is, both of these teams are stuck in mediocrity. They are 6th seeds at best, and that's asking a lot, especially for the Wolves (in the West). Therefore, they must build for the future. And if you're stuck in mediocrity, and you know so, and you can choose between a 25 year old superstar, and a slightly better 30 year old, who would you pick? Obviously the 25 year old, because you'd have more time to build around him.