Custom fields date before 1900

[Irsan]

I have created a custom field type date for my products, in my case stamps. Some stamps are dated before 1900. Currently, my virtuemart installation uses a date format is mm/dd/yy so when I try to input Dec-05-1898 I use 12/04/98 which is converted to 1998. How can I use dates before 1900?

Irsan