How do I create a date of birth field with adult control in checkout?

// Display Billing birthdate field to checkout and My account addresses
add_filter( 'woocommerce_billing_fields', 'display_birthdate_billing_field', 20, 1 );
function display_birthdate_billing_field($billing_fields) {

    $billing_fields['billing_birthdate'] = array(
        'type'        => 'date',
        'label'       => __('Geburtsdatum'),
        'class'       => array('form-row-wide'),
        'priority'    => 25,
        'required'    => true,
        'clear'       => true,
    );
    return $billing_fields;
}

// Save Billing birthdate field value as user meta data
add_action( 'woocommerce_checkout_update_customer', 'save_account_billing_birthdate_field', 10, 2 );
function save_account_billing_birthdate_field( $customer, $data ){
    if ( isset($_POST['billing_birthdate']) && ! empty($_POST['billing_birthdate']) ) {
         $customer->update_meta_data( 'billing_birthdate', sanitize_text_field($_POST['billing_birthdate']) );
    }
}

// Admin orders Billing birthdate editable field and display
add_filter('woocommerce_admin_billing_fields', 'admin_order_billing_birthdate_editable_field');
function admin_order_billing_birthdate_editable_field( $fields ) {
    $fields['birthdate'] = array( 'label' => __('Geburtsdatum', 'woocommerce') );

    return $fields;
}

// WordPress User: Add Billing birthdate editable field
add_filter('woocommerce_customer_meta_fields', 'wordpress_user_account_billing_birthdate_field');
function wordpress_user_account_billing_birthdate_field( $fields ) {
    $fields['billing']['fields']['billing_birthdate'] = array(
        'label'       => __('Geburtsdatum', 'woocommerce'),
        'description' => __('', 'woocommerce')
    );
    return $fields;
}

// Check customer age
add_action('woocommerce_checkout_process', 'check_birth_date');
function check_birth_date() {
    // Check billing field
    if( isset($_POST['billing_birthdate']) && ! empty($_POST['billing_birthdate']) ){
        // Get customer age from birthdate
        $age = date_diff(date_create($_POST['billing_birthdate']), date_create('now'))->y;

        // Checking age and display an error notice avoiding checkout (and emptying cart)
        if( $age < 18 ){
            wc_add_notice( __( "Du musst mindestens 18 Jahre alt sein, um in unserem Shop bestellen zu können!" ), "error" );

            WC()->cart->empty_cart();
        }
    }
}