Here ya go...
<?PHP
$date = '01-10-1984'; # mm-dd-yyyy
list ($month, $day, $year) = split('-', $date);
$starttime = mktime(0, 0, 0, $month, $day, $year);
$today = time();
$timepassed = $today-$starttime;
$days = floor($timepassed/(60*60*24));
echo $days.' days have passed since the significant event.';
?>