Board Thread:Support Requests - Getting Started/@comment-31376609-20170223180517/@comment-27345308-20170223181222

You can't make only administrators edit. Wikis are community projects meant for public audience, protecting a whole wiki from being edited would be a Terms of Use violation.

If you don't want your wiki to be edited by everybody, you should just make sure nobody has the link to it. First step would be removing it from Favourite Wikis section on your profile :P