I think it would be a lot better used if you didn't have to activate it through the UserCP. Surely it would be better to have it automatically active for individuals aged over 18 and have a notice saying that people have to select their age to over 18 to view them.
That way new members would simply read the notice and select their age if they wanted to view them; if they are too young or don't want to view them, they simply don't put in their age. That would increase activity in the section IMO as I don't think a lot of people know it is there.