Hey! Here is my another wordpress plugin. Using this plugin, you can mention a post as inappropriate for non-adult and ask viewer his/her before showing the content to him. If age given age is below your Minimum Age requirement (configurable from settings page), then the viewer can’t see the content.
Moreover, a cookie is set so that persistent tries also restrict from seeing the content. Allmost everything of the plugin can be reconfigured from plugin configuration page.
This plugin is tested with WordPress 2.6.2 and 2.7
Feedback is appreciated.