Age Restrictions for Adult Account?

You changing their Privacy Settings from Child to Adult doesn't change the account status to adult itself. So pretty much their accounts are still child. It will be possible to change it to adult as soon as they reach 18. If that is the age of an adult in
your country ofc. You cannot change that setting manually. The restriction on downloadable content stays locked until they reach the required age depending on the content age restriction.

You may have set the account as adult but is your age set to that of an adult? That may be why its restricted.

Is you account an adult or child account.

As child accounts wont be able to play them as they have a age restriction.

Hopefully you're an adult now. Since you are on an age restriction, the master account (who put the restriction on you) will need to sign in and lift it.

I found this, hope it helps.

Promote a child account to an adult account in Xbox

Xbox LIVE determines whether an account is a child account or an adult account based on the age of the account owner. Account owners who are younger than 18 are given child accounts in the United States. The legal adult age varies by country and region (for
example, the adult age in Korea is 20).

Child accounts are tied to an adult's Microsoft account. The adult account can control Family Settings and restrict some features of Xbox LIVE.

After you reach the age of adulthood (which varies by country and region), you can promote a child account to an adult account. This promotion removes the Family Settings and Xbox LIVE restrictions.

To promote a child account to an adult account

Sign in to Xbox LIVE by using the account that you want to change.

Go to Settings, and then select Account.

Select Promote Child Account.

Note The age of an account owner is calculated by using the date of birth provided when the account was created. This date cannot be changed. If you entered an incorrect date of birth when you created the account, your only option is to create a new account
using the correct date of birth. This option is available only if the date of birth for the account indicates that you have reached the age of adulthood (18 in the United States). The legal adult age varies by country and region.

Follow the on-screen instructions to promote the account.