Вот мое решение, оно не идеально, но все же хорошо для моей проблемы:
//Setting datepicker :
birthday.setDayCellFactory(picker -> new DateCell() {
@Override
public void updateItem(LocalDate date, boolean empty) {
super.updateItem(date, empty);
//Setting date 18 years ago
LocalDate today = LocalDate.ofYearDay(LocalDate.now().getYear() - 18, LocalDate.now().getDayOfYear());
//Disable future date
setDisable(empty || date.compareTo(today) > 0);
}
});
//Setting actual value
birthday.setValue(LocalDate.ofYearDay(LocalDate.now().getYear() - 18, LocalDate.now().getDayOfYear()));
//Cover the value by text
String pattern = "dd-MM-yyyy";
formatCalender.format(pattern, birthday);
birthday.getEditor().setText("Date Of Birth");
birthday.setPromptText(null);