Is there a way I can make this script run sub_scripts simultaneously

Yes, use Parallel::ForkManager to fork off multiple processes.

Something like this (adapted from the docs):

use Parallel::ForkManager;

...

    my $pm = new Parallel::ForkManager(10);   # max 10 processes simul
+taneously

    foreach my $job_id (keys %$results) {
        $pm->start and next; # do the fork

        system("perl -w script.pl $job_id");

        $pm->finish; # do the exit in the child process
    }
    $pm->wait_all_children;
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(Note: due to the usage of system() in the child processes, you'd in fact be running twice the number of processes.  If you want to avoid this (and are not doing anything with system()'s return status anyway), you could also use exec("perl -w script.pl $job_id"); in which case the $pm->finish would not be required (though it doesn't do any harm to leave it there, for when the exec should fail for some reason...).)

Update: note to whoever downvoted (which I suppose was because of the comment on using exec):  if you have doubts, do try it before you downvote :)  It does work just fine, because in the above case, finish simply calls CORE::exit.  If you have evidence to the contrary, show it!