In such situations, I find it helpful to use Data::Dumper to see what the data really looks like (if necessary), and then break the final dereference into multiple lines for clarity and simplicity, as well as ease-of-use for further operations:

use Data::Dumper;

%people=( 
'Jones'=>{'name'=>'Alison', 'age'=>15, 'pet'=>'dog',},
'Smith'=>{'name'=>'Tom', 'age'=>34, 'pet'=>'cat',});
foreach $person (keys %people)
{
    my $person_attributes = $people{$person};

    # Use Data::Dumper here to be *sure* of the data format
    # of the variable $person_attributes.
    #
    # printf "Person attributes:  %s\n", Dumper(\$person_attributes);

    # Display the values ...
    my @attributes = values %$person_attributes;
    printf "Attributes:  %s\n", join(",", @attributes);

    # ... or make use of one or more attributes ...
    my $age = $person_attributes->{'age'};
    do_something_with_age($age);    # Process this person's age

    # ... or process all of the attributes together
    do_something_with_this_person($person_attributes);
}
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