Add extra checkboxes in Woocommerce user register form and saving / showing if are checked in the backend as user extra data

I would like to show in the backend, when seeing the user detail if the checkboxes were selected when the user was created, here is the code that helped me to implement the extra checkboxes in the register form.

function woocommerce_edit_my_account_page() {
    return apply_filters( 'woocommerce_forms_field', array(
        'woocommerce_my_account_page' => array(
            'type'        => 'checkbox',
            'label'       => __( 'Soy mayor de 18'),
            'required'    => true,
        ),
        array(
            'type'        => 'checkbox',
            'label'       => __( 'Le doy permiso de usar mis datos'),
            'required'    => true,
        ),
    ) );
}
function edit_my_account_page_woocommerce() {
    $fields = woocommerce_edit_my_account_page();
    foreach ( $fields as $key => $field_args ) {
        woocommerce_form_field( $key, $field_args );
    }
}
add_action( 'woocommerce_register_form', 'edit_my_account_page_woocommerce', 15 );

Answer

There is a mistake in your first function as each checkbox needs it own $key to be saved.

Here is your revisited code that will first validate that mandatory checkboxes, save values and display them in the admin User dashboard:

function registration_custom_checkboxes() {
    return apply_filters( 'woocommerce_forms_field', array(
        'age_ckeck' => array(
            'type'        => 'checkbox',
            'label'       => __("Soy mayor de 18", "woocommerce"),
            'required'    => true,
        ),
        'permission_ckeck' => array(
            'type'        => 'checkbox',
            'label'       => __("Le doy permiso de usar mis datos", "woocommerce"),
            'required'    => true,
        )
    ) );
}

// Display checkboxes in Registration form
add_action( 'woocommerce_register_form', 'add_registration_custom_checkboxes', 15 );
function add_registration_custom_checkboxes() {
    foreach ( registration_custom_checkboxes() as $field_key => $field_args ) {
        woocommerce_form_field( $field_key, $field_args );
    }
}
// Validation for mandatory checkboxes in Registration form
add_action( 'woocommerce_register_post', 'registration_custom_checkboxes_validation', 10, 3 );
function registration_custom_checkboxes_validation( $username, $email, $validation_errors ) {
    $fields = registration_custom_checkboxes();
    foreach ( array_keys($fields) as $field_key ) {
        if ( ! isset( $_POST[$field_key] ) {
            if ( $field_key === 'age_ckeck' ) {
                $validation_errors->add( $field_key . '_error', __("You need to approve that your are at leats 18 years old.", "woocommerce") );
            } else {
                $validation_errors->add( $field_key . '_error', __("You have to allow us to use your data.", "woocommerce") );
            }
        }
    }
    return $validation_errors;
}

// Save registration checkboxes fields values
add_action( 'woocommerce_created_customer', 'save_registration_custom_checkboxes_values' );
function save_registration_custom_checkboxes_values( $customer_id ) {
    $fields = registration_custom_checkboxes();
    foreach ( array_keys($fields) as $field_key ) {
        if ( isset( $_POST[$field_key] )  ) {
            update_user_meta( $customer_id, $field_key, '1' );
        }
    }
}


// Admin WP User: Display checkboxes fields on user profile
add_action ( 'show_user_profile', 'display_user_custom_checkboxes_fields' );
add_action ( 'edit_user_profile', 'display_user_custom_checkboxes_fields' );
function display_user_custom_checkboxes_fields( $user ){
    echo '<h3>'.__("Age and permission checks", "woocommerce").'</h3>';
    foreach ( registration_custom_checkboxes() as $field_key => $field_args ) {
        woocommerce_form_field( $field_key, $field_args, get_user_meta( $user->id, $field_key, true ) );
    }
}


// Admin WP User: Update checkboxes fields values
add_action( 'personal_options_update', 'save_user_custom_checkboxes_values' );
add_action( 'edit_user_profile_update', 'save_user_custom_checkboxes_values' );
function save_user_custom_checkboxes_values( $user_id ) {
    $fields = registration_custom_checkboxes();
    foreach ( array_keys($fields) as $field_key ) {
        $value = isset( $_POST[$field_key] ) ? '1' : '0';
        update_user_meta( $user_id, $field_key, $value );
        // error_log( ('Key: ' . $field_key . ' | posted: ' . $_POST[$field_key] . ' | value: ' . $value) );
    }
}

Code goes in functions.php file of the active child theme (or active theme). Tested and works.