If member posted in forumX within X months, then member has access to that forum.

[Alfa1]

I want to restrict a certain forum to members which have posted in that forum within the last x months.
How do I do this? Is there a hack for this or is someone willing to code this?

I assume that the access to forum X can be created by an addition member group, which is granted based upon conditionals? I would love to learn your view on this.

[josh_B]

Try user promotions. You can set to x posts and min of x days registered on the forum. You can also use reputation level and so on..

[Alfa1]

That has nothing to do with this. If I am being unclear, please ask.
Just to be sure:
I want to restrict a forum to members which keep posting there. Anyone who stops posting there for some time should loose access to that forum.