Here is a way to do it with Date::Manip, although as far as I can tell your string does not contain a valid 'date'--because it does not specify a day. So you have to alter your string first:

use strict;
use warnings;
use 5.010;

use Date::Manip::Date;

my $string = 'Nov-07';
$string .= ' 01';  #add day field to string
my $format = '%b-%y %d';

my $date = new Date::Manip::Date;
my $error = $date->parse_format($format, $string);

if ($error == 0) {  #everything worked correctly
    say $date->printf('%Y/%m');
}
else { 
    say "something went wrong";

    if ($error == 1) {
        say "format didn't match your string";
    }
    else {
        say "format is invalid--won't create a valid date: $error";
    }
}

--output:--
2007/11
[download]

See here for details:

http://search.cpan.org/~sbeck/Date-Manip/lib/Date/Manip/Date.pod