SMF allows to set up permissions for Post-Count based membergroups. Enabling this options the permission for each member will vary depending on the user's number of posts.

This option can be enabled from Admin > Members > Permissions > Settings, selecting Enable permissions for post count based groups and saving.

Once enabled, going to Admin > Members >Permissions > General Permissions all the post-count based membergroups will be listed along with the normal membergroups. Selecting Modify next to the membergroup of interest it will be possible to define specific permissions for each and every post-count based membergroup.

Please note that revoking a permission to a membergroup doesn't necessarily mean that members belonging to this membergroup will be unable to perform such action, please see Category:Permissions#About_Permissions and What is the difference between disallow and deny in permissions for details.