How to change my account age? With no parent account?

There is no way to have support change it.

The date of birth on Xbox Live accounts cannot be changed.

The date of birth on Xbox Live accounts cannot be changed.

what if some one from the support team changed it?

changing the dob nor the info at the live.com site doesn't affect the xbox account as the age of the account is set at the date of creation of the xbox account

not being able to change the age of the account is a good thing it prevents kids from removing parental settings that their parents set

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.