use v5.20;
use warnings;
use File::Find;
use File::stat;

...

find(sub{
  my $stat= stat $_ or die "stat($_): $!";
  say "unlink $_" if time - $stat->mtime > 30*60;
}, $folder);
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When you are really sure it unlinks the right files, replace say "unlink $_" with unlink $_.