Alert Aging alows you to postpone the generation of alert notifications. This is done when you configure the subscriptions for your notifications. Alert Aging has been designed so that it works on the basis that if the state hasn’t changed for X minutes (X being the delay you have defined) then send the notification. Unfortunately if you have Closed notifications setup this also means that once an alert has remained in the Closed state for X minutes then a notification is still sent. I have been unable to find away around this if you need Open and Closed notifications.
The screenshot below shows where Alert Aging is configured:-