A regex that checks values like that is going to be far too complex to maintain. You're better off using a function that checks for valid dates. The timelocal function from Time::Local, converts a list of values (like those returned from localtime) into a epoch seconds value and it dies if passed an invalid date. You can use eval to catch and report on those errors.

#!/usr/bin/perl

use strict;
use warnings;

use Time::Local;

while (<DATA>) {
  chomp;
  my ($y, $m, $d) = split /-/;

  eval { timelocal 0, 0, 0, $d, $m-1, $y-1900 };

  if ($@) {
    print "$_ is not a valid date\n";
  } else {
    print "$_ is a valid date\n";
  }
}

__DATA__
2006-10-30
2006-10-32
2006-02-29
2004-02-29
[download]

It's simple enough to wrap that up into a is_valid_date function.