Smarty Modifier - Calculate age from birth date

modifier.calculate_age.php

<?php
   /**
    * Smarty plugin
    *
    * @package Smarty
    * @subpackage PluginsModifier
    * Place this file inside the smarty/libs/plugins directory and invoke as any other modifier (e.g. {$birth_date|calculate_age} )
    */

   /**
    * Smarty date_format modifier plugin
    *
    * Type:     modifier<br>
    * Name:     calculate_age<br>
    * Purpose:  Calculate age based on a given date<br>
    * Input:<br>
    *          - string: date in the YYYY-MM-DD format
    *
    * @author Ivan Melgrati
    * @param string|\DateTime The birth date
    * @return int The actual age. If the birthdate is not a DateTime object cannot be converted to one, -1 will be returned
    */
   function smarty_modifier_calculate_age($date)
   {
       $age = 0;

       $clean_date = null;

       if (is_a($date, 'DateTime')) {
           $clean_date = $date;
       } else {
           if (is_string($date)) {
               $dirty_date = new \DateTime(trim($date));
               if (is_a($dirty_date, 'DateTime')) {
                   $clean_date = $dirty_date;
               } else {
                   // Wrong format. Creation date set to null and returns a null result.
                   $clean_date = null;
               }
           }
       }

       if (is_a($clean_date, 'DateTime')) {
           $age = date_diff($clean_date, date_create('now'))->y;
       }
       else
       {
           $age = -1;
       }
       return $age;
   }
?>