Diane Poremsky wrote:

use this method:
http://www.outlook-tips.net/howto/countdown.htm

Unfortunately, that requires an infinite number (well, until the person
dies, anyway) of individual calendar entries instead of a single recurring
event. Moreover, if you have the birthday field defined in the contact
record and you modify that record at all, Outlook will readd the recurring
event and produce duplicate entries in the day/week/month views.
--
Brian Tillman [MVP-Outlook]