PHP $_GET - Retrieving Data via URL

<form action="" method="get">
    <div class="simulator-info">
        <h3>Sending data via GET</h3>
        <label for="name">Name:</label><br>
        <input type="text" id="name" name="name"><br>
        <label for="age">Age:</label><br>
        <input type="number" id="age" name="age"><br>
        <label for="city">City:</label><br>
        <input type="text" id="city" name="city"><br><br>
        <button type="submit">Send to URL</button>
    </div>
</form>

.simulator-info { padding: 20px; border-left: 5px solid #4CAF50; }
h3 { margin-top: 0; color: #2e7d32; }
input { padding: 5px; margin: 5px 0; border: 1px solid #ccc; }

<?php
if (isset($_GET["name"]) && isset($_GET["age"]) && isset($_GET["city"])) {
    $name = $_GET["name"];
    $age = $_GET["age"];
    $city = $_GET["city"];

    echo "Name: " . $name;
    echo "Age: " . $age;
    echo "City: " . $city . "<br>";
    echo "<b>URL result:</b> ?name=" . $name . "&age=" . $age . "&city=" . $city;
}
?>