use strict;
use warnings;

my @startDates =
   qw(01-06-2007 01-08-2006 01-06-2006 01-07-2007 06-01-2007);

my $leastDate =
   (
      map  {join q{-}, reverse split /-/}
      sort
      map  {join q{-}, reverse split /-/}
      @startDates
   )[0];

print qq{Least date is $leastDate\n};

##</code><code>##

Least date is 01-06-2006