Automatically Close Comments on Old Posts

function close_comments_on_old_posts($posts) {
    if (!is_admin()) {
        $days_old = 30; // Change this to your desired number of days
        foreach ($posts as $post) {
            if (strtotime($post->post_date) < strtotime("-$days_old days")) {
                $post->comment_status = 'closed';
                $post->ping_status = 'closed';
            }
        }
    }
    return $posts;
}
add_filter('the_posts', 'close_comments_on_old_posts');