function showHideWarning(e) {
  if($F('Age') == 'Under 16' && $F('Mentor') == 'on') {
    $('ageWarning').show();
  }
  else {
    $('ageWarning').hide();
  }
}

function enableDisableShare(e) {
  if($F('Mentor') == 'on') {
    $('Share').enable();
  }
  else {
    $('Share').disable();
  }
}

Event.observe(document, 'dom:loaded', showHideWarning);
$('Age').observe('change', showHideWarning);
$('Mentor').observe('click', showHideWarning);
$('Mentor').observe('keypress', showHideWarning);

Event.observe(document, 'dom:loaded', enableDisableShare);
$('Mentor').observe('click', enableDisableShare);
$('Mentor').observe('keypress', enableDisableShare);