@list = (
  {fname => 'Jan', lname => 'Krynicky', 
   birth_date => 'Sep 3 1975', #... 
  },
  {fname => 'Pavel', lname => 'Krynicky', 
   birth_date => 'Dec 25 1969', #... 
  },
  {fname => 'Martin', lname => 'Krynicky', 
   birth_date => 'Aug 24 1973', #... 
  },
);

##</code><code>##

use Date::Calc qw(Decode_Date_US);
use Data::Dumper;

sub convertdate {
	return sprintf '%04d%02d%02d', Decode_Date_US($string)
}

# ST
@sorted = map{
    $_->[1]
} sort{
   $a->[0] <=> $b->[0]
} map{
    [ convertdate($_->{birth_date}), $_ ]
} @list;

print Dumper(\@sorted);


# @keys array
{
	my @keys = map convertdate($_->{birth_date}), @list;
	@sorted = @list[ sort {$keys[$a] cmp $keys[$b]} (0..$#list) ];
}

print Dumper(\@sorted);

# GRT
@sorted = map{
 ## Chop off the bit we added.
    substr( $_, 8 )
} sort map{           ## Note: No comparison block callback.
    ## Extract the field as before, but concatenate it with the original element
    ## instead of building an anonymous array containing both elements.
    convertdate($_->{birth_date}) . $_
} @list;

print Dumper(\@sorted);

##</code><code>##

$VAR1 = [
          'HASH(0x18db494)',
          'HASH(0x224e9c)',
          'HASH(0x224fa4)'
        ];