use strict;
use warnings;

while (<DATA>)
{
   if (/\d{2}-\d{2}-\d{4}\s+/)
   { 
       print;
   } 
}   

=Prints:
03-15-2021 21.1.0-s102 2021/03/15:04:00:09 21.1 21.10-s102
21.1.0-s102 2021/03/15:04:00:09 21.1 21.10-s102 03-15-2021  **works**
=cut

__DATA__

03-15-2021-1 21.1.0-s103 2021/03/15:14:16:39 21.1 21.10-s103
03-15-2021-2 21.1.0-s103 2021/03/15:14:16:39 21.1 21.10-s103
03-15-2021 21.1.0-s102 2021/03/15:04:00:09 21.1 21.10-s102
21.1.0-s102 2021/03/15:04:00:09 21.1 21.10-s102 03-15-2021
21.1.0-s102 2021/03/15:04:00:09 21.1 21.10-s102 03-15-2021-4