use loop to return blog details

You need to re-arrange your code.

<?php 
        $post_id = 20;

        while($post_id <= 25) {
            $queried_post = get_post($post_id); 

            $author_id = $queried_post->post_author;
            echo get_the_author_meta('display_name', $author_id);


            $post_id++;
        } 
?>

Within while loop above you have $queried_post which is an object of class WP_Post. Member Variables of WP_Post can be used to display data about each post.

I hope this may help.

UPDATE

what if i want to the loop to apply to all of the post that there are on the site. What would be the changes i would need to make in order for me to apply to all the posts?

In that case you may code like that using get_posts() which returns an array of objects

<?php 
        $arg = array( 'numberposts' => -1 );  // get all posts

        $queried_posts = get_posts( $arg);

        // Now loop through $queried_posts
        foreach( $queried_posts as $queried_post ) {

            $author_id = $queried_post->post_author;
            echo get_the_author_meta('display_name', $author_id);

        } 
    ?>