[Dygear]

Your options are to place all of these users who have their date of birth set as Jan 1st 1901, add them to a user group that you have made up. Then Make a new notice that only that usergroup can see. From there, tell them they have to update their data of birth.

Your other options are, you can convert these values your self if you still happen to have the old database, parse the date, and convert if for each user on your forum.

Anything else would require a modification of the vB default install, and since we are not all playing with the same deck anymore I can't really help you there.