Hi,
this one of most common customer's requirements which is not implemented out-of-the-box yet...
at this time the only thing you can do is to vote up for idea (I have found more than 5 idea's about date validation properties, but this looks more flexible): Regular Expression in Properties
Otherwise, if you have a little JavaScript experiense you can try to implement it by yourself. Property's build script located in detail_form.js.
Regards,
cdtj