Age Restriction on an Xbox Account

Yes, I figured it out. For whatever reason, there was an age restriction on my Xbox account, probably for my little brother. Anyway, removing the age restriction and trying again worked for me. Try checking if you have any restrictions at all on your account
(Xbox or Microsoft) and remove them. This should work for you too.

I've tried everything

I assume you are trying to change your age in order to get around parental restrictions?

If so, even if you could change the age on your account, it won't accomplish getting around parental restrictions.

Your Xbox account will always remember the age originally entered in at account creation so even if you change your age from that if a child to an adult for instance, you will still have parental restrictions.

While you can change the preferences in family settings to control a childs privacy and such, some games or their publishers have their own restrictions based on the account age. That age is deterined by the age of the Xbox account. Your family preferences will not overide restrictions set by the game publishers or the service providers (Xbox). For example, I think it is EA that restricts some online content to 13yrs and older. That cannot be changed via family preferences.

Do you have any age restrictions on the Xbox live account?

If you are logged into your YouTube account while browsing the YouTube app, age restrictions might apply to the signed-in YouTube/Google+ account. If not, then it is probably getting age details from your Xbox Live account.

Either way, you'll need to make sure your birthdate settings are consistent between accounts and you are of legal age to watch restricted videos.