The "18+" usergroup is a specialized usergroup that allows its members to view restricted content of the site (art, pictures, fanfiction, etc).
The only way to join the 18+ usergroup is to contact the forum Administrators in the special thread. Keep in mind that we are unable to verify your age, so its up your honesty and dignity. The only requirement for the 18+ usergroup members is to have the Community Member status or higher (exceptions may apply at the discretion of Staff). We will keep you posted with any updates on this matter.