function getAgeFromBday() {
  var month = document.getElementById('bdc-month').value;
  var day   = document.getElementById('bdc-day').value;
  var year  = document.getElementById('bdc-year').value;
  var bdate = new Date(year, month, day);

  if (bdate.getDate() != day || bdate.getMonth() != month || bdate.getFullYear() != year) {
    alert('That date appears to be invalid!');
    return false;
  }

  var today = new Date();
  today.setHours(0);
  today.setMinutes(0);
  today.setSeconds(0);

  if (bdate > today) {
    alert('Provided date must fall before today\'s date!');
    return false;
  }

  alert(Math.floor((today - bdate) / 31556952000));
}