#!/usr/bin/perl -w
use strict; 

use XML::Twig;

# initialize the index document
# pretty_print => 'indented' gives you exactly the output you showed
my $index= XML::Twig->new( pretty_print => 'record_c')
                    ->parse( '<friends/>');
my $friends= $index->root;

foreach my $file (@ARGV)
  { my $friend; # the current friend
    my $t= XML::Twig->new(      
             start_tag_handlers => { # create a new friend in the index
                                     person => sub { $friend= $friends->insert_new_elt( last_child => 'person') } 
                                   },
             twig_roots         => { # store the elements in the friend
                                     'person/name' => sub { $_->move( last_child => $friend); },
                                     'person/age'  => sub { $_->move( last_child => $friend); }
                                   }
                         )
                    ->parsefile( $file);
  }
$index->print;