Date::Calc is just working as advertised. In the docs, it's stated that Delta_YMD returns the vector [y2 - y1], [m2 - m1], [d2 - d1]. So the negative value is understandable.

Even taking absolute values, however, this is still sort of worthless because it lacks accountability for months with differing day counts, etc. The real way to do it is subtract your seconds since epoch and work back to YMD from the result.

Here's an example using Time::Piece and Time::Seconds:

#!/usr/bin/perl

use Time::Piece;
use Time::Seconds;

$bd_time = Time::Piece->strptime("1973/07/19", "%Y/%m/%d");
$now = localtime(time);

$diff = $now - $bd_time;

$years  = int($diff->years);
$diff  -= $years * ONE_YEAR;
$months = int($diff->months);
$diff  -= $months * ONE_MONTH;
$days   = int($diff->days);

print "$years years, $months months, $days days\n";
[download]

Today that yields 29 years, 1 month, 17 days. Use Lingua::EN::Inflect to season your output. Serves 4.

Matt