public function setMaxAge($max_age, $shared_max_age = null)
    {
        $cache_control = $this->getCacheControl();

        $cache_control['max-age'] = (int) $max_age;

        if(!is_null($shared_max_age) && $shared_max_age > $max_age) {
            $cache_control['s-maxage'] = (int) $shared_max_age;
        }

        $this->_headers->set('Cache-Control', $cache_control);

        return $this;
    }