use warnings;
use strict;
use DateTime;
use DateTime::Format::Strptime;

my $date_birth = '21/02/2013';
my $diab_confirm = '29/08/2013';

my $strp = DateTime::Format::Strptime->new(on_error=>'croak',
	pattern => '%d/%m/%Y');

my $dt_birth = $strp->parse_datetime($date_birth);
my $dt_confirm = $strp->parse_datetime($diab_confirm);
print "   birth: ", $dt_birth->ymd, "\n";
print " confirm: ", $dt_confirm->ymd, "\n";

my $dt_deadline  = $dt_birth->clone->add(months=>6);
print "deadline: ", $dt_deadline->ymd, "\n";

if ($dt_confirm > $dt_deadline) {
	print $dt_confirm->ymd, " > ", $dt_deadline->ymd, "\n";
}
else {
	print $dt_confirm->ymd, " <= ", $dt_deadline->ymd, "\n";
}

__END__

   birth: 2013-02-21
 confirm: 2013-08-29
deadline: 2013-08-21
2013-08-29 > 2013-08-21