Subtraction Broken?

[Matthew McGillis]

I'm not sure if I'm doing something really wrong or if things are 
broke but with this code:

#!/usr/bin/perl

use DateTime;

$birth=DateTime->new(year=>1968,month=>6,day=>28);
print $birth->ymd."\n";
$today=DateTime->today;
print $today->ymd."\n";
$age=$today-$birth;
print $age->years."\n";
I get this output:

1968-06-28
2003-08-17
0
That zero sure doesn't seem correct to me.