use HTML::TreeBuilder;
my $tree = HTML::TreeBuilder->new();
$tree->parse_file($filename);
$tree->age_handler($age);
print $tree->as_HTML;

sub age_handler {
   my ($tree, $age) = @_;
   my $SPAN = $tree->look_down('id', 'age_handler');
   if ($age < 10) {
	$SPAN->look_down('id', $_)->detach for qw(under18 welcome);
   } elsif ($age < 18) {
	$SPAN->look_down('id', $_)->detach for qw(under10 welcome);
  } else {
        $SPAN->look_down('id', $_)->detach for qw(under10 under18);
  }

}