Manual:$wgAutoConfirmAge

Details
Sets the number of seconds an account is required to age before it's given the implicit 'autoconfirmed' group membership. Note that the user must pass $wgAutoConfirmAge and $wgAutoConfirmCount to become a member of that group.

This can be used to limit privileges of new accounts. Accounts created by earlier versions of the software may not have a recorded creation date, and will always be considered to pass the age test.

When left at 0 (the default), all registered accounts will pass.

Some other useful settings: