Magento DOB widget with DOB Validation

dob.phtml

<?php
/**
 * @see Mage_Customer_Block_Widget_Dob
 */
?>
<label class="dob-label" for="<?php echo $this->getFieldId('month')?>"<?php if ($this->isRequired()) { echo ' class="required"'; } ?>><?php echo $this->__('Birthday') ?></label>
<div class="customer-dob input-box">
    <div class="dob-year">
        <?php $currentYear = intval(date("Y")); ?>
        <select name="<?php echo $this->getFieldName('year'); ?>" id="<?php echo $this->getFieldId('year'); ?>">
            <option value="">YYYY</option>
            <?php for ($i = $currentYear; $i >= $currentYear - 60; $i--): ?>
                <option value="<?php echo $i; ?>" <?php echo ($i==$this->getYear()) ? "selected" : ""; ?>><?php echo $i; ?></option>
            <?php endfor; ?>
        </select>
    </div>

    <div class="dob-month">
        <select name="<?php echo $this->getFieldName('month'); ?>" id="<?php echo $this->getFieldId('month'); ?>">
            <option value="">MM</option>
            <?php for ($i = 1; $i <= 12; $i++): ?>
                <?php $month = (strlen($i) == 1) ? "0".$i : $i; ?>
                <option value="<?php echo $month; ?>" <?php echo ($i==$this->getMonth()) ? "selected" : ""; ?>><?php echo $month; ?></option>
            <?php endfor; ?>
        </select>
    </div>

    <div class="dob-day">
        <select name="<?php echo $this->getFieldName('day'); ?>" id="<?php echo $this->getFieldId('day'); ?>">
            <option value="">DD</option>
            <?php for ($i = 1; $i <= 31; $i++): ?>
                <?php $day = (strlen($i) == 1) ? "0" . $i : $i; ?>
                <option value="<?php echo $day; ?>" <?php echo ($i==$this->getDay()) ? "selected" : ""; ?>><?php echo $day; ?></option>
            <?php endfor; ?>
        </select>
    </div>

    <div class="dob-full" style="display:none;">
        <input type="hidden" id="<?php echo $this->getFieldId('dob')?>" name="<?php echo $this->getFieldName('dob')?>" />
    </div>
    <div class="validation-advice" style="display:none;"></div>
</div>
<script type="text/javascript">
    //<![CDATA[
    var DOBSelects = Class.create(Varien.DOB, {
        initialize: function(selector, required, format) {
            var el = $$(selector)[0];
            var container       = {};
            container.day       = Element.select(el, '.dob-day select')[0];
            container.month     = Element.select(el, '.dob-month select')[0];
            container.year      = Element.select(el, '.dob-year select')[0];
            container.full      = Element.select(el, '.dob-full input')[0];
            container.advice    = Element.select(el, '.validation-advice')[0];
            new Varien.DateElement('container', container, required, format);
        }
    });
    var customer_dob = new DOBSelects('.customer-dob', <?php echo $this->isRequired() ? 'true' : 'false' ?>, '<?php echo $this->getDateFormat() ?>');

    var year  = $('year');
    var month = $('month');
    var day   = $('day');

    function daysInMonth(month,year) {
        var dd = new Date(year, month, 0);
        return dd.getDate();
    }

    function setDayDrop(dyear, dmonth, dday) {
        var year  = dyear.options[dyear.selectedIndex].value;
        var month = dmonth.options[dmonth.selectedIndex].value;
        var day   = dday.options[dday.selectedIndex].value;
        var days  = (year == '' || month == '') ? 31 : daysInMonth(month,year);

        dday.options.length = 0;
        dday.options[dday.options.length] = new Option('DD','DD');
        for (var i = 1; i <= days; i++){
            dday.options[dday.options.length] = new Option(i,i);
        }
    }

    function setDay() {
        setDayDrop(year,month,day);
    }

    year.observe('change', setDay);
    month.observe('change', setDay);
    //]]>
</script>

The original gist was from https://gist.github.com/iamncla/7794502 but it seems to have evaporated. I have hence modify it to include DOB validation in displaying the relevant days for each month based on what month was selected.

Hello @dele454, like your code and I'm on my website, but now would like to implement validation of 18 years old would like help me??

I researched and found some topics, but did not succeed in implementing:
http://magento.stackexchange.com/questions/9037/age-verification-varien-dateelement-vs-varien-dob
http://blog.speedupmate.com/post/54662500786/magento-wrap-date-of-birth-frontend-validation

Already grateful for the attention.

good post it work proper