Well as an admin, your the one who owns or controls the forum. If you decide to have an 18+ forum then that is your responsibility to deal with. This mod is an age lock; it is supposed to stop those underage from entering the forum, its not a mod to "hide" the forums, I agree with Stuie, there is no point to that. Just put your members straight dont be bullied by those under 18. Its simple your forum says "over 18's" only. Plus its obviously 18+ for a reason most likely involving the law, so really there is no arguement.
Its like going into a porn shop under 18 and complaining to the shopkeeper you can't buy anything. You can see the shop and what it is, but are under age to purchase; tough luck. You wouldnt go inside kicking up a fuss now lol
Ive had great success with this mod, my forum says clearly its 18+ for a reason and ive had no complaints or "drama". The ironic thing is; most of my members are under 18 anyway