OS X Mavericks: When there are no users to manage
All users of this Mac are administrators or sharing-only users, so you can’t use parental controls to manage them. Do one of the following:
Select “Create a new user account with parental controls.”
Select “Convert this account to a parental controls account.” This option converts the account you’re currently using to a regular, non-administrator account. If this Mac has only one administrator, you’ll also be prompted to create a new administrator to replace the one you’re converting. OS X requires at least one administrator.
If you don’t want to do either option, click Show All to return to System Preferences, or click the close box.
To limit the activities of people who use your Mac without adding them as users, set up a guest user with parental controls. For more information, see: