I'm not an expert in Moose, but looking at it makes me wonder why you are referencing it. I took the reference to age out of the sub.

sub show_person {
   my $self = shift;
   return $self->name();
}
[download]

If it's not required, then it wasn't necessary to return it, at least to my way of thinking. My logic could be off, which happens frequently, but here's the code that I ran. It returns "Bob" with no warnings.

package Person;
use Moose;

has 'name' => ( is  => 'ro', isa => 'Str', required => 1);
has 'age'  => ( is  => 'ro', isa => 'Str');

sub show_person {
   my $self = shift;
   return $self->name();
}

__PACKAGE__->meta->make_immutable;
no Moose;
1;

my $person = Person->new(name => "Bob");
print $person->show_person(), "\n";
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