#!/usr/bin/perl
use strict;
use warnings;

my %hoh = (
 kevin => {
   age   => "12",
   favorite_color       => "blue",
   gender       => "boy",
 },
 john => {
   age   => "11",
   favorite_color       => "green",
   gender       => "boy",
 },
 lisa => {
   age   => "11",
   favorite_color       => "pink",
   gender       => "girl",
 },
 sara => {
   age   => "13",
   favorite_color       => "purple",
   gender       => "girl",
 },
 shelly => {
   age   => "12",
   favorite_color       => "purple",
   gender       => "girl",
 },
);
my %counts;
my $key = 'age';
foreach my $person (values %hoh) {
    $counts{$person->{$key}}++;
}
use Data::Dumper;
print Dumper(\%counts);