Normally when a knowledge entry is created it will be up to readers to decide if it needs updating. However, you can also set the knowledge entry workflow to automatically have members with the right permission notified when an entry has been published for a certain number of days and might need reviewing.
To do this, in the space go to Settings, choose the Advanced settings tab and then the Knowledge entry workflow option. Change the setting to the number of days required - a good choice might be a year or half year. When it is that number of days old, a new task will be created in My tasks that lets members with the permission to activate entries decide if it should continue being published or returned to editing.