process.php

<?php

function para($msg) { echo "<p>$msg</p>"; }

function error($msg) {
    $valid = false;
    para($msg);
}

$name = trim($_REQUEST["name"]);
$email = trim($_REQUEST["email"]);
$age = trim($_REQUEST["age"]);
$comments = trim($_REQUEST["comments"]);

$valid = true;

if (!preg_match('/[A-Za-z\-\.]{1,20}/', $name)) {
    error("Name should only contain letters, hyphens and dots and no more than than 20 characters.");
}
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    error("Your email is invalid.");
}
if (!preg_match('/\d{2}/', $age)) {
    error("Your age is invalid.");
}
if (empty($comments)) {
    error("You have not entered your comments.");
}

if ($valid) {
    para("Thank you");
    para("Name: $name, Email: $email, Age: $age");
    para("Comments");
    para($comments);
}

?>