How to make sure a string contains more then automatically inputed defaults?

I have an input form to create a customField name, when the page loads the textbox is automatically filled with "cst_".

I preset this value in my class:

class customField{

    // DEFINE PROPERTIES
    public $id = 0;
    public $groupId;
    public $name = 'cst_';
    public $displayName;
    public $type;
    public $defaultValue;
    public $required;
    public $orderCount;
    ...

When I go to save the fields on my page, I check to make sure that the user has imputed more values than just leaving the "cst_"

I do this by simply:

// CHECK FOR ONLY "cst_"
if(strlen($customField->name > 4)){

    // SAVE
    $customField->save();

}else{ noticeSet(1,'PLEASE ADD NAME');noticeSet(1,strlen($customField->name));}

in my textbox I added cst_water hardness however I get the error

PLEASE ADD NAME

18

I don't understand how it is failing at that if statement

I've added a noticeSet before the if statement and it shows 18.

Is there any better way to see if a user has added more than just "cst_"?