#!/usr/bin/perl -w
use strict;
use DateTime;

my $date = [ 
    qw{ 
      06/30/96
      08/07/97
      09/05/97
      12/11/97
      03/26/98
      07/17/98
      10/23/98
      11/12/98
      01/14/99
      04/10/99
      05/27/99
      02/10/00
      03/10/00
      03/15/00
      03/15/00
      03/30/00
      06/15/00
      07/13/00
      08/03/00
      09/07/00
      09/30/00
      12/10/00
      01/25/01
      02/27/01 }
];

my $oldest = dt( shift @$date );

printf "Diff in month between %s and \n", $oldest->dmy('/');
printf "%s : %s\n",  $_, dt($_)->subtract_datetime($oldest)->in_units('months') for @$date;

sub dt {
    my ( $month, $day, $year ) = split /\//, shift;
    $year = ( $year > 90 ? '19' : '20' ) . $year;
    DateTime->new( year => $year, month => $month, day => $day );
}