OK, sell it over Xbox Live, Wiiware, or the Playstation Network.
I'm not sure about Live but all the games in PSN and the Wii store seem to be rated by the ESRB
The gamestop in my town just says. "Okay have a good time" one you buy it.No lectures nothing. Not even you're not old enough to purchase this.
I don't think the ESRB rates Indie games on Xbox Live.