Update code snippet of wc-kco-validate-customer-age.php to only accept purchases from people over 18 years

wc-kco-validate-customer-age-modded.php

<?php 
/**
 * Title: WooCommerce - Klarna payment gateway (Modded)
 * Author Niklas Hogefjord
 * Editor: Mattias Ghodsian
 * Description: Only accept purchases from customer over 18 years of age.
 * Source: https://gist.github.com/NiklasHogefjord/07e60a4f08799c3cfdb0870fb5481f71
 * Klarna: https://developers.klarna.com/en/se/kco-v2/checkout-api
 * Donate a cup of coffee: https://www.buymeacoffee.com/mattiasghodsian
 **/

/**
 * Edit the order data sent to Klarna to make 'Date of birth' a mandatory field in the KCO iframe
 */
add_filter('kco_create_order', 'my_kco_create_order');
function my_kco_create_order( $create ) {
	// not sure wtf this is.
	$create['options']['national_identification_number_mandatory'] = true;
	// enable KCO pno checkout page
	$create['options']['date_of_birth_mandatory'] = true;
	return $create;
}

/**
 * Validate the customers age on the validate callback from Klarna (happens right before the purchase is finalized).
 * The 'Check items stock and valid shipping method during checkout' setting needs to be checked in the KCO settings for this to work.
 * The store needs to have SSL/https enabled for the validate callback to work.
 */
add_action('kco_validate_checkout', 'my_kco_validate_checkout' );
function my_kco_validate_checkout( $data ) {
	// $data is the returned order data sent from Klarna
	$birthday = new DateTime($data['customer']['date_of_birth']);
	$now = new DateTime();
	$age = $now->diff($birthday);
	if( $age -> y < 18 ) {
		header( 'Location: ' . wc_get_checkout_url() . '?under_age' );
		exit();
	}
}

/**
 * Display an error notice above the KCO checkout if the customer is under 18 years.
 */
add_action('klarna_before_kco_checkout', 'my_klarna_before_kco_checkout' );

/*
 * add KCO error to normal woocommerce checkout
 */
add_action('woocommerce_before_checkout_form', 'my_klarna_before_kco_checkout' );
function my_klarna_before_kco_checkout() {
 	if ( isset( $_REQUEST['under_age'] ) ) {
		echo '<div class="woocommerce-error">';
		_e( 'You need to be over 18 years to make a purchase.', 'woocommerce-gateway-klarna' );
		echo '</div>';
	}
}
?>