HOW DO YOU CHANGE YOUR AGE ON XBOX LIVE?

I WANT TO DOWNLOAD DEMOS BUT IT WONT LET ME SO HOW DO YOU CHANGE YOUR AGE ON XBOX LIVE???HOW DO YOU CHANGE YOUR AGE ON XBOX LIVE?Sadly you cant do that. MS doesnt allow to change the date of birth once its entered. So if you want to download any demos %26amp; addons then I would suggest you to create a new gamertag.