Unable to access Xbox Insider Hub

Thanks for your quick reply.

He is unable to unenroll as he cannot launch the Insider Hub anymore because it states that his account needs to be an adult account. He doesn't understand how he was able to install it a year ago as he's always used
his child account. We don't have a pc, is it possible to access the insider hub on a Mac? Or perhaps login on a browser? Although, won't he have the same issue on whatever device he instals the insider hub on, that he has a child account?

Only certain members of the Xbox Insider Hub have access to the Minecraft Beta

Accessing the higher ring levels in the Insider program requires you actively participate in the provided Insider Hub "quests", submit regular feedback and bug reports, fill out surveys and polls, and use your console
often.

In this program, the most dedicated users to the Insider Hub will be able to access the Alpha and Beta rings, which get them the privilege of bug-testing the cutting-edge feature implementations first.

More reading:

- All About the Insider Hub:
https://support.xbox.com/en-US/xbox-one/console/xbox-insider-program

- Insider Hub Forums: http://aka.ms/XboxInsiderForums

You can't be a member of the insider program if you have had any enforcement action on your account within the past 12 months.

Not to sure why they would send you back to general forum support, because Xbox Forum support can't access any information regarding your status in the Xbox Insider program. I would suggest you chat with a Xbox Preview support member using the "Chat with
support People in line: x" feature on the forum I listed above. That will get you directly to a Xbox Preview team member who should be able to get the exact answer to why you can't join, or at least pass your account along to someone who manages registration
that can.