用php传递变量的问题

$name = $_GET['name'];
$age = $_GET['age'];

<form action="index.php" method="post">
 <input type="text" name="name" value="John">
 <input type="text" name="age" value="25">
 <input type="submit" value="Submit">
</form>

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

session_start();

$_SESSION['name'] = 'John';
$_SESSION['age'] = 25;

session_start();
$name = $_SESSION['name'];
$age = $_SESSION['age'];

setcookie('name', 'John', time()+3600);
setcookie('age', 25, time()+3600);

$name = $_COOKIE['name'];
$age = $_COOKIE['age'];