Update post date of page when Visitor access that page?

You can hook into the action the_post (you get the post as parameter here) and run wp_update_post(). Make sure to clean up the date properties and not to run on the admin side or when a post is called in a widget:

is_admin() or add_action( 'the_post', function( $post ) {

    if ( ! is_singular() or ! is_main_query() )
        return;

    $post->post_date     = current_time( 'mysql' );
    $post->post_date_gmt="";

    wp_update_post( $post );
});

But now you get a write operation on every single request. This will slow down your site. I wouldn’t do that.