Sort products by date asc

function enable_catalog_ordering_by_modified_date( $args ) {
    if ( isset( $_GET['orderby'] ) ) {
        if ( 'modified_date' == $_GET['orderby'] ) {
            return array(
                'orderby'  => 'modified',
                'order'    => 'ASC',
            );
        }
    }
    return $args;
}

add_filter( 'woocommerce_get_catalog_ordering_args', 'enable_catalog_ordering_by_modified_date' );

function add_catalog_orderby_by_modified_date( $orderby_options ) {
    // Rename 'menu_order' label
    $orderby_options['modified_date'] = __("Sort by oldest", "woocommerce");

    return $orderby_options ;
}

add_filter( 'woocommerce_catalog_orderby', 'add_catalog_orderby_by_modified_date' );