User function construct user.class

I'm trying to create my user.class.php constructor but I don't know really much about POO so I'm going to tell you what I'm doing and I hope you could help me.

user.class.php

class user {
    private $fullname;
    private $age;
    private $email;
    private $sex;
    private $nacionality;

        public function __construct($usrId){
            $mysqli = new connection_mysqli(); // I've already implemented this and it works.
            $query = "SELECT * FROM USERS WHERE USER_ID = $userId";
            if ($result = $mysqli->query($query)) {
               $userData = $result->fetch_assoc(); 
               $this->fullname = $userData['fullname'];
               $this->age = $userData['age'];
               $this->email = $userData['email'];
               //.....
            }
        parent::__construct($usrId);

    }
}

What I'm going to do on my index.php is this:

index.php

<?php
include('scripts/class/user.class.php');
$user = new user($_SESSION['userid'];
echo $user->fullname;
?>

So, is this going to work right? is this well programmed? any tip? Thanks for your time.