use utf8; does not enable Unicode output - it enables you to type Unicode in your program. Add this to the program, before your print() statement:

binmode(STDOUT, ":utf8");

See if that helps. That should make STDOUT output in UTF-8 instead of ordinary ASCII.

You want to use the -newermt option for find:

find /media/WD/backup/osool/olddata/ -newermt 20120101 -not -newermt 20130101

to get all the files with modification time in 2012.