Here's one approach, using a Schwartzian Transform:

sub parse {
  my $item = shift;
  return [ $item, $item =~ /^(\d+)([a-zA-Z]*)/ ];
}

sub sort_alphanum {
  $a->[ 1 ] <=> $b->[ 1 ] or
  $a->[ 2 ] cmp $b->[ 2 ];
}

my @sorted =
  map $_->[ 0 ],
  sort sort_alphanum
  map parse( $_ ), @old;
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It's only merit (if any), relative to the other solutions posted, is that it illustrates a relatively general approach to this type of problem. It's most useful when the extraction of the parameter(s) to sort by (in this case, the job done by the parse sub) is costly.