Im making this tutorial because i wasted too much time searching this and maybe help someone!
I used a jquery that use css to add a maxlength to textarea. So:
1- First, install the free plugin 'jQuery++ Integrator' to integrate joomla and jquery
To load jquery faster put jquery.js at the root of the site:
1.1- Config embed jquery to: Yes - Local copy
1.2- Config jQuery custom CDN to: /http://index.php/jquery-1.6.2.js (just an example)
2- Download jquery.maxlength.js (search at google) and put at the root of the site.
3- Between <head> </head> of the index.php of your template use this:
<script type="text/javascript" src="jquery.maxlength.js"></script>
<script>
jQuery(document).ready(function($) {
$().ready(function(){
$("#jevcontent"

});
});
</script>
3.1- Edit #jevcontent to the css that you want.
3.2- Edit 178 to the maxlength that you want.
3.3- If you want more just add another code like:
$("#example"

$("#jevcontent"

4- Good luck! Bye.