By default, as you enter dates in a workbook, the dates are formatted to display two-digit years.
Change the way two-digit years are interpreted
Caution This procedure changes the way two-digit years are interpreted for all the Microsoft Windows programs that you have installed.
As you change the upper-limit year, the lower-limit year automatically changes.
Change the default date format to display four-digit years
When you change the default date format to a different format by using this procedure, the display of dates that were previously entered in your workbook will change to the new format as long as the dates haven't been formatted by using the Cells command (Format menu).