hiding forums based on user age

[hinch]

I assumed this was a fairly common issue but appears I was wrong

I want to create an "after hours" forum section as part of my public forums however I want it to not show up for unregistered users or registered users below the age of 18.

Now my plan was to have an admin editable only custom field that is simply a 1 or a 0 for above or older that way I have to verify that they are over 18 instead of just taking their word for it (way to cover my ass legally )

What I can't seem to work out how todo is make a forum visible/invisible based off the value of a custom user profile field.

Is there any known way of doing this or perhaps a better way of doing this?