#!/usr/bin/perl
use strict;
use warnings;
use feature qw{ say };

my %age_of = (John  => 20,
              Jane  => 19,
              Jack  => 21,
              Jules => 22,
              Jim   => 18);

my $whose_birthday = 'Jane';

$age_of{$whose_birthday}++;
say "Happy birthday $whose_birthday, you're now $age_of{$whose_birthday}!";