If you want to pre-disable Gutenberg for when it launches, install the following plugin, activate and untick the checkbox in the settings: https://wordpress.org/plugins/classic-editor/

If you also want to avoid the 5.0 update, you can always hide the update banner:

//Add to functions.php file to remove WordPress update notice 

function hide_update_notice() {
remove_action( 'admin_notices', 'update_nag', 3 );
}
add_action( 'admin_notices', 'hide_update_notice', 1 );