How to redirect a specific user after log-in?

I want to redirect an user and his user ID is 6. So I added this code into my functions.php

if ( is_user_logged_in() ) {
    $user_id = get_current_user_id();
      if ($user_id == 6) {
            /* redirect users to front page after login */
            function redirect_to_front_page() {
                global $redirect_to;
                    if (!isset($_GET['redirect_to'])) {
                    $redirect_to = get_option('siteurl');
                    }
                }
            add_action('login_form', 'redirect_to_front_page');             
      }
    }   

But still the user goes to the rpofile page after the log-in. How can I get it works?

[update]
Then I’ve tried to change to username instead of user ID but still same. He gets profile page after login.
like this:

function redirect_to_front_page() {
    global $redirect_to;
    if ( is_user_logged_in() ) {
        //$user_id = get_current_user_id();
        $current_user = wp_get_current_user();

          //if ($user_id == 6) 
          if ($current_user->user_login = 'hirer') {
            /* redirect users to front page after login */
            if (!isset($_GET['redirect_to'])) {
                $redirect_to = get_option('siteurl');
            }
        }

    }
}
add_action('login_redirect', 'redirect_to_front_page');  

still nothing changed. The user gets profile page when he login.

You need to use the login_redirect filter returning the redirect location:

add_filter( 'login_redirect', 'redirect_to_home', 10, 3 );
function redirect_to_home( $redirect_to, $request, $user ) {

    if( $user->ID == 6 ) {
        //If user ID is 6, redirect to home
        return get_home_url();
    } else {
        //If user ID is not 6, leave WordPress handle the redirection as usual
        return $redirect_to;
    }

}