Simple character counter with a custom min and max comment length. Not much in the way of validation, just something simple.

index.html

<form id="enquiry" action="">
  <textarea maxlength="140" name="message" id="message" placeholder="Add your comment!"></textarea>
  <input type="submit" value="Add Comment">
</form>
​

script.js

$(document).ready(function () {
    var comment = $('form#enquiry textarea'),
        counter = '',
        counterValue = 140, //change this to set the max character count
        minCommentLength = 10, //set minimum comment length
        $commentValue = comment.val(),
        $commentLength = $commentValue.length,
        submitButton = $('form#enquiry input[type=submit]').hide();
  
    $('form').prepend('<span class="counter"></span>').append('<p class="info">Min length: <span></span></p>');
    counter = $('span.counter');
    counter.html(counterValue); //display your set max length
    comment.attr('maxlength', counterValue); //apply max length to textarea
    $('form').find('p.info > span').html(minCommentLength);
    // everytime a key is pressed inside the textarea, update counter
    comment.keyup(function () {
      var $this = $(this);
      $commentLength = $this.val().length; //get number of characters
      counter.html(counterValue - $commentLength); //update counter
      if ($commentLength > minCommentLength - 1) {
        submitButton.fadeIn(200);
      } else {
        submitButton.fadeOut(200);
      }
    });
  });

style.css

body {
 background: #444; 
 font-family: 'Open Sans', sans-serif;
}

form {
 position: relative;
 top: 40px;
 border-radius: 4px;
 width: 400px;
 height: 180px;
 margin: 0 auto;
}

form textarea {
 border-radius: 2px;
 box-shadow:  0px 2px 11px 0px rgba(0, 0, 0, 0.3);
 border: 1px solid #e2e6e6;
 margin: 10px 0 10px 0;
 font-family: 'Open Sans', sans-serif;
 outline: none;
 width: 395px;
 height: 100px;
}

form span.counter {
 float: right;
 color: #f2f2f2;
}

form p.info {
 font-size: 11px;
 color: #999;
}
form p.info > span {
 color: #fff; 
}

form input[type=submit] {
 cursor: pointer;
 box-shadow:  0px 2px 11px 0px rgba(0, 0, 0, 0.3);
 border: 1px solid #A8F1FF;
 border-radius: 2px;
 background-color:#0093B0;
 color: #fff;
 float: right;
 padding: 10px;
}
​