Redirect tag archives to specific pages?

Hi,
I came across this bit of code and am wondering what I’m doing wrong…

add_action( 'template_redirect', 'my_redirect_term_to_post' );

function my_redirect_term_to_post() {
	global $wp_query;

	if ( is_tax() ) {
		$term = $wp_query->get_queried_object();

		if ( 'posttag' == $term->taxonomy ) {
			$post_id = my_get_post_id_by_slug( $term->slug, 'post' );

			if ( !empty( $post_id ) )
				wp_redirect( get_permalink( $post_id ), 301 );
		}
	}
}

function my_get_post_id_by_slug( $slug, $post_type ) {
	global $wpdb;

	$slug = rawurlencode( urldecode( $slug ) );
	$slug = sanitize_title( basename( $slug ) );

	$post_id = $wpdb->get_var( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_name = %s AND post_type = %s", $slug, $post_type ) );

	if ( is_array( $post_id ) )
		return $post_id[0];
	elseif ( !empty( $post_id ) );
		return $post_id;

	return false;
}

Basically I want the user to click on the tag at the bottom of a post, and have them be redirected to a page that has the same slug as the tag itself. I added this code to m functions.php file but it’s not working and I’m a bit of a n00b!