Should be under the Wiki options section. It's not visible if the Wiki is marked for content for children.

How can i make my wiki not for children

If the Wiki actually doesn't host content for children, you can contact staff here. If it is, then it should not be changed.

^why it can't be changed

It can. You just need to contact staff to do so.

Why have you bothered to share the link to your home Wiki’s Admin Dashboard? Only local admins can see that and so every outsider from the Wiki who clicks on that link won’t have access as none of us here are likely to have elevated rights of any kind on your home Wiki.