XBox marketplace restrictions?

I'm trying to download the demo for Duke Nukem Forever (yes, I know it's sh*tty but I still want to try it), but when I try to download it a message comes up that reads, "This account is not permitted to download content with this rating." My Family Settings are turned off, and even if they were turned on I've set everything so that I can download anything, no matter what it is rated. I've had this problem since I got XBox live, which was about 3 years ago. I feel like I've tried everything, and I have no clue what I can do to fix this. Can anyone help?