<script type="text/javascript" charset="utf-8">  
  $(document).ready(function() {
 
    // Identify this question
    var thisQuestion = $('#question{QID}');
 
    $('#movenextbtn').hide();
 
    // Check the initial value of the age question
    if($('input.text', thisQuestion).val() != '' &amp;&amp; $('input.text', thisQuestion).val() < 18){
      $('#movenextbtn').show();
    }
 
    // A listener on the age question
    $('input.text', thisQuestion).on('keyup change paste', function() {
      setTimeout(function() {
        if($('input.text', thisQuestion).val() != '' &amp;&amp; $('input.text', thisQuestion).val() < 18){
          $('#movenextbtn').show();
        }
        else {
          $('#movenextbtn').hide();
        }
      }, 100);
    });    
  });
</script>