I see the problem now, sorry, it was my fault, forgot to put the end of the if statement inside of php
<?php
if (get_field('data_of_birth', false, false)) {
// get raw date
$date = get_field('date_of_birth', false, false);
// make date object
$date = new DateTime($date);
echo $date->format('M j, Y'); ?> (<?php
$date = get_field('date_of_birth');
$birthday = new DateTime($date);
$interval = $birthday->diff(new DateTime);
echo $interval->y.' years old';
?>)<?php
} // end if date
?>
