#!/usr/bin/env perl

use strict;
use warnings;
use feature qw (say);

my @dates = qw{
  12112014
  01052015
  02202015
  03102015
  01012011
  04092015
  09092015
};

my $max_date = 0;
my $result;

for (@dates) {
    my $date = join "", reverse unpack q(a4a4);
    $result = $_ and $max_date = $date if $date > $max_date;
}
print $result;