No Admin Columns Showing

I've tried adding some admin columns to a CPT but they won't output at all. What am I doing wrong?

 public function generateMetaBox($meta_boxes){
        // General
        $meta_boxes[]=array(
            'id'=>'general',
            'title'=>'General Person Settings',
            'post_types' => 'people',
            'context'    => 'normal',
            'priority'   => 'high',
            'fields'=> array(
                array(
                    'name'  =>  'Job Title',
                    'id'    =>  'people_jobtitle',
                    'type'  =>  'text',
                    'desc'=>'TODO: help text',
                    'admin_columns' => 'after title'
                ),
                array(
                    'name'=>'Year Joined',
                    'id'=>'people_yearjoined',
                    'desc'=>'TODO: help text',
                    'type'=>'number',
                    'min'   =>  1980,
                    'max'   =>  date('Y'),
                    'admin_columns' => true,
                ),
            )
        );

        return $meta_boxes;
    }