1st : Tell us what you want from this script: 

I suppose it's : make someone enter a date until what he/she
types is a "good" date (in "good" format). right ? 

If yes, you loop until the entry is OK ?

2nd : the format you show is not clear  : 
      It could be : 2008, January the 1st 
                    2001, January the 8th, ... and so on
It should be better to write it MM-DD-YY (for month, day, year).  (FYI :I'm french and we display dates as DD/MM/YY)

for this format, the regex "could" be:
(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])-\d\d 
but : it ignores that the maximum number of days depends on the month(28,29,30,31), it ignores leap years (February 28th  or 29 th ?)

You should use the function "timelocal()" from the standard module
 "Time::Local" : try to transform the date you have to validate into an "epoch" time (as the function time() returns) : if the function fails, the date is wrong : 
this script seems to work:

use Time::Local timelocal;
my ($m,$d,$y);
do
{
    my $date;
    print "date (MM-DD-YY) ? ";
    $date=<>;
    chomp($date);
    ($m,$d,$y)=split(/-/,$date); 
    $m -= 1;
    $y += 1900;
}
until(timelocal(0,0,0,$d,$m,$y));