The minimum age requirement is set when an event is first created using the event creation wizard. If you copy an event, the settings will copy over to the new event.
To edit the age restriction after the event is already created, go to OPEN EVENTS and select MANAGE EVENT DATES from the drop-down menu. Click the date and then edit the age restriction. Click each date to edit the age restriction per event date.
If using an event scheduler, the age setting is on the scheduler. Under MANAGE EVENT DATES click the scheduler and edit the age requirement. The change will take effect for NEW event dates created using the scheduler. Events dates already created will not be updated.