Displaying age in popbox leads to "unable to load tooltip"

I am trying to achieve showing the age inside the popbox. This works fine but not all the time. Some profiles show "unable to load tooltip" but most profiles are working. I am trying to find out what causes this problems. Maybe someone can help?

What I did so far:

I have edited "components/com_easysocial/themes/wireframe/profile/popbox/user.php" and added the following code:

<?php

$id = JRequest::getInt( 'id' , null ); 

// current user profile id 

$user = Foundry::user($id); 

// Get your current birthday custom field unique key e.g. BIRTHDAY 

$birthdayDate = $user->getFieldValue('BIRTHDAY'); 

// Pass birthday date into this section 

$birthDate = new DateTime($birthdayDate); 

$now = new DateTime(); 

// Use this formula generate to age 

$age = floor(($now->format('U') - $birthDate->format('U')) / (60*60*24*365)); 

echo "($age)"; 

// Result

?>

From line 9 on there seems to be a problem but due to my nearly non-existent programming skills I am not able to find it...