Whats wrong with this php Birthday converter?

[Blue]

I get "Fatal error: Call to undefined method DateTime::diff() in /var/www/BD-Check.php on line 4"

The code is
<?php
$birthdate = new DateTime("5-3-1204");
$now = new DateTime("now");
$difference = $birthdate->diff($now);
echo "Age: " + $difference->format("%y years, %m months and %d days!");
?>

Whats wrong with this?

 

[elpasi2]

You need to have PHP 5.3?

The DateTime object is available in 5.2, but diff is only in 5.3.