#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my %hash = (
        Matt => 24, Dana => 19, Eric => 28, Sara => 20, John => 17, Mike => 23,
);

if (%hash)
{
        my (@min, @max);

        while( my ($k,$v) = each %hash )
        {
                @min = ($k,$v) unless @min && ($v > $min[1]);
                @max = ($k,$v) unless @max && ($v < $max[1]);
        }

        $hash{$min[0]} = $max[1];
        $hash{$max[0]} = $min[1];
}

print Dumper \%hash;