Well, there is some code at http://www.slipstick.com/contacts/calcage.htm
which can calculate the person's age in a custom field if you enter their
birthdate on the Details tab, but you won't see that information in your
appointment for their birthday.
Personally, when adding birthdays to my calendar, I put the year of the
person's birth in square brackets after the word "Birthday" -- for example,
Mary's Birthday [1957]. Don't use parentheses around the year -- Outlook
may treat the year as a Location for the event.

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Jocelyn Fiorello
MVP - Outlook
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> I'd like Outlook to display a contact's age (calculated from their date of
> birth in the "birthday" field using code for a custom field which can be
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> Contacts.
> Any ideas? Thanks!