How do I change my age for my Xbox Live account?

I want to download Left 4 Dead 2 demo on Xbox Live, but it says I'm not permitted to because of my age. I have the dumb family settings on and when I tell it that I can play all games with all ratings it still says it. I want to know how I can change my age so I can download the demo or something.How do I change my age for my Xbox Live account?Yup, to download this kind of stuff you need to register as 18+.How do I change my age for my Xbox Live account?you can not change your age once you have made the account. the only way for you to play those demos and stuff is to make a whole new account with an 18+ age on it.How do I change my age for my Xbox Live account?you can't sorry m8 you have to make a new accountHow do I change my age for my Xbox Live account?yeah you cant