$user_data{$username}={"date of birth"=>$dob,
                       "ID number"=>$idnum,
                       "mailing address"=>[$street,
                                           $citystatezip,
                                          ],
                       };

##</code><code>##

$user_dob{$username}=$dob;
$user_idnum{$username}=$idnum;
$user_mailaddress{$username}=[...];