add_action( 'cmb2_init', 'yourprefix_register_about_page_metabox' );
function yourprefix_register_about_page_metabox() {

	// Start with an underscore to hide fields from custom fields list
	$prefix = '_yourprefix_about_';

	/**
	 * Metabox to be displayed on a single page ID
	 */
	$cmb_about_page = new_cmb2_box( array(
		'id'           => $prefix . 'metabox',
		'title'        => __( 'About Page Metabox', 'cmb2' ),
		'object_types' => array( 'page', ), // Post type
		'context'      => 'normal',
		'priority'     => 'high',
		'show_names'   => true, // Show field names on the left
	) );

	$cmb_about_page->add_field( array(
		'name' => __( 'Test file', 'cmb2' ),
		'desc' => __( 'field description (optional)', 'cmb2' ),
		'id'   => $prefix . 'image',
		'type' => 'file',
	) );

 	$cmb_about_page->add_field( array(
		'name' => __( 'Test image list', 'cmb2' ),
		'desc' => __( 'field description (optional)', 'cmb2' ),
		'id'   => $prefix . 'imagelist',
		'type' => 'file_list',
	) );

}