$myDb = new mysqli($hostname, $username, $password, $database);

if($myDb->connect_errno > 0){
    die('Unable to connect to database [' . $myDb->connect_error . ']');
}

$statment = $myDb->prepare("INSERT INTO user(name,surname,age)
VALUES (?,?,?)");
  $statement->bind_param('s', $_POST['name']);
  $statement->bind_param('s', $_POST['surname']);
  $statement->bind_param('i', 25);


  $statement->execute();

  $statement->free_result();

Binding parameters failed: (0) Execute failed: (2031) No data supplied for parameters in prepared statement

$myDb = new mysqli($hostname, $username, $password, $database);

if($myDb->connect_errno > 0){
    die('Unable to connect to database [' . $myDb->connect_error . ']');
}

$statment = $myDb->prepare("INSERT INTO user(name,surname,age)
VALUES (?,?,?)");
  $statement->bind_param('s', $name);
  $statement->bind_param('s', $surname);
  $statement->bind_param('i', $age);

$name = $_POST['name'];
$surname = $_POST['surname'];
$age  = 25;


  $statement->execute();

  $statement->free_result();

$myDb = new mysqli($hostname, $username, $password, $database);

if($myDb->connect_errno > 0){
    die('Unable to connect to database [' . $myDb->connect_error . ']');
}

$statement = $myDb->prepare("INSERT INTO user (name,surname,age) VALUES (?,?,25)");
$statement->bind_param('ss', $_POST['name'], $_POST['surname']);

$statement->execute();

$statement->free_result();
$statement->close();