domain age

<?php

function domain_age($domain) {
    // TODO: return the age of the domain in years
    $whois = "whois $domain";
    $txt = shell_exec($whois);
    $start = explode("Creation Date: ", $txt);
    $end = explode("\n", $start[1]);
    $date =  $end[0];
    $date_array = explode("/", $date);
    $year = $date_array[2];
    $current_year = date("Y");
    $age = $current_year - $year;
    return $age;
}

echo domain_age("google.com"); // returns "18"
echo domain_age("bbc.co.uk"); // returns "28"
echo domain_age("github.com"); // returns "9"
echo domain_age("facebook.com"); // returns "13"