How do I turn off parental controls on an Xbox One that was purchased from someone that had...

Hi,

it's not allowed to buy or sell a Xbox with accounts on it.

I recommend you to perform a full factory reset immediately !

Hi Chezney,

I'm Anirban and I'll be happy to help you.

In this case I recommend to do factory reset to the console. Here are the steps:

1. Press the Xbox button to open the guide.
2. Select Profile & system > Settings > System > Console info.
3. Select Reset console.
On the Reset your console screen, you'll see three options:

choose "Reset and remove everything"

After you select one of the options, your Xbox console begins the process of erasing the selected content and resetting itself to the default settings.

source: https://support.xbox.com/en/help/hardware-network/console/reset-console-to-factory-defaults

kind regards

You cannot change the age but you can turn off Parental Controls. See:
support.xbox.com/.../parental-control for the steps (that document tells you how to turn them on but it is the same steps for turning them off... You can see the Off option in the image).

Have you got a family account setup at all, or parental controls?

That may be the issue.

Try asking your parent/guardian to turn off their parental controls, and reply if it does not help.

If your parent/guardian does not know how to turn parental controls off, tell them to promote the Xbox Live account to an adult one, instead of a child one. You may have a child account, instead of a full adult account.

Please see this post
forums.xbox.com/.../224525.aspx