Yet another option could be with Time::Piece (a core module now):

#!/usr/bin/perl
use strict;
use warnings;

use Time::Piece;

my $datf = Time::Piece->strptime("1/1/1904", "%d/%m/%Y");
my $datt = Time::Piece->strptime("5/3/2013", "%d/%m/%Y");

my $diff = $datt - $datf;
my $result = $diff->days + 1462;
print "$result days\n";
[download]

This prints "41338 days".