you will need to hand code it.
change:
<?php
for($y=date('Y'); $y>=date('Y')-100; $y--){ ?>
<option value="<?php echo $y; ?>"><?php echo $y; ?></option>
<?php } ?>
to:
<?php
for($y=date('Y'); $y>=date('Y')-100; $y--){ ?>
<option value="<?php echo $y; ?>" <?php if (!(strcmp($y, (ValidatedField("pagename","year"))))) {echo "selected=\"selected\"";} ?>><?php echo $y; ?></option>
<?php } ?>