Hi Cari,
I don't think you can do this with the validation pattern, you would have to use some script.
Is it possible to use a drop down list, with the years as values? You could use some code like this in the preOpen event to populate the values (which populates the last 20 years);
var d = new Date()
var years = []
for (var y = new Date(d.getFullYear() - 20, 0, 1); y.getFullYear() <= d.getFullYear(); y.setFullYear(y.getFullYear()+1)) {
years.push(y.getFullYear());
}
this.setItems(years.join(","));
Regards
Bruce