<?php
/**
 * Created by PhpStorm.
 * User: rahman
 * Date: 11/4/14
 * Time: 5:09 AM
 */

Validator::extend('must_alpha_num', function($attribute, $value, $parameters)
{
    $ret = FALSE;
    if (preg_match("/^[A-Za-z][A-Za-z0-9]{5,31}$/", $value)) {
        $ret = TRUE;
    }
    return $ret;
});
<?php
/**
 * Created by PhpStorm.
 * User: rahman
 * Date: 11/4/14
 * Time: 5:09 AM
 */

Validator::extend('must_alpha_num', function($attribute, $value, $parameters)
{
    return !is_numeric($value);
});
--- 
+++ 
@@ -8,5 +8,9 @@
 
 Validator::extend('must_alpha_num', function($attribute, $value, $parameters)
 {
-    return !is_numeric($value);
+    $ret = FALSE;
+    if (preg_match("/^[A-Za-z][A-Za-z0-9]{5,31}$/", $value)) {
+        $ret = TRUE;
+    }
+    return $ret;
 });
Fix username validation alphanumeric only
