How do i change my age on xbox live ?

Im trying to download a couple demos of Xbox 360 marketplace. But im only 17 ( you have to be 18 ). Is there a way to edit my profile or create a new one that says im 18 ? Id prefer a way that doesnt require me to buy a 2nd 12+1 month gold subscription for a 2nd account. What should i do.How do i change my age on xbox live ?i tried it before and i couldn't find a way, someone said you might be able by changing your email address then changing your age or something like that.