New forum suggestions are among the least used suggestions. The site owner purposefully minimizes the number of forum groups to keep the choices simple. As well as to prevent too much division.
Even within the existing groups all are able to post within them, even those that don't fit into to group. Such as in the Teens forums adults are able to post there as well. The only forum group to be isolated is the Women's forum.
So even if it were created it would likely be open to everyone, like the rest of the site. The forum topics help to centralize specific discussions, not be exclusive areas.
Also, volunteering to be a mod (overseeing any part of the site) automatically locks you out of a chance at becoming one.