Can you change an account to an adult account when you don't have a family group?

No one in the forums is going to be able to help with that. You can try contacting Xbox Support but you will have to provide significant information about the account.

Use this link to contact Xbox Support https://beta.support.xbox.com/contact-us

Hi Fellow gamer,

Thanks for coming to the forums. If the account is a child account there is no way of changing it through the websites. As the birthdate on Xbox.com is not changeable. However if you are over the age of 18 you can submit proof of age to change it. If you
are not, you will need to wait until the account graduates (hits the age of 18).

You can submit an Age verification Form,you
can also submit proof of age.



After submitting this form, you will receive email confirmation and follow up emails. Also will get instructions on how you monitor the status of your request. Please do not fill out multiple requests. You can expect an email response usually
within 3 days.



Hope this helps, please let us know how it goes.



Thanks

Brad

Problem is I dont have an adult account and dont have a family group

You will then need an adult to create an account, add you to the family group and then change those settings for you, to enable you to play:

https://support.microsoft.com/en-us/help/12417/microsoft-account-add-members-to-family

In this case, have an adult go through his or her Microsoft account and invite you to a family group so he or she can manage your privacy settings.

If you don't have a family group, the steps to create one below:
Visit family.microsoft.com.

1. Select Create a family group. Sign into or create a Microsoft account.
   
2. Add family members by email or phone number to create your family group.
   

Once the adult adds you to the family group, they should visit the website: https://account.xbox.com/en-us/settings
The adult must have his account logged in at the moment, and then he will see your profile and his, he must change the settings of your profile, in the case of the child.

Hi, Zach.

The message appears only when an account is a child account.

It is important to mention that removing an account from a family group will not remove those restrictions.

I can advise you to re-join your family group and ask the adult account that added you to change your privacy settings when needed to do in the potential solution I shared.