Manual:$wgAutoConfirmAge

Details
Number of seconds an account is required to age before it's given the implicit 'autoconfirm' group membership.

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: