My son got one when he was 5 yo. He plays it occasionally when he's ready to wind down.
I think people have it in their mind that kids who own them will be playing them all the time. I think if parents can show self-control and discipline it doesn't have to be this way at all. My son is sporty, active, creative, fun, loud... but he will play his DS a few times a week for maybe half an hour after a day of sports/school and I see absolutely no problem with this.