This isn't exactly what you want, but it (Data::Rmap) is new to my toolbox and quite handy if your structure becomes more mangled:

use strict;
use warnings;
use Data::Rmap qw(:all);

my @AoH = (
    {'name' => 'Barney', 'age' => '34'},
    {'name' => 'Fred', 'age' => '36'},
    {'name' => { first => 'John', last => 'Doe' }, age => '40' }
);

rmap_hash {
    print join "\n" => keys %$_;
    print "\n";
} @AoH;
[download]

name
age
name
age
name
age
first
last
[download]