If I were you. I would get him a Gameboy Color, or Advanced (if you can find one) and get some old school pokemon games (red, blue, yellow). Much better than DS's
We already have those :-P. Actually my step-sons are both fans of oldschool games. I was impressed at their dedication at beating every old Mario game.
They're up to Mario 64. That's a tough one! I don't think I've ever beaten it to be honest.