To see how to do this and just about everything else you might want to do with dates in Word, check out my Microsoft Word Date Calculation Tutorial, at:
http://windowssecrets.com/forums/sho...ation-Tutorial
or
http://www.gmayor.com/downloads.htm#Third_party
In particular, look at the item titled 'Calculate the # Years Months & Days Difference Between Two Dates'. Do read the document's introductory material.