Found a third bug. $_ isn't the variable you should be using. $_ is relative to some path relative under /Users/admin/Documents/ScriptTest/, but you're trying to rename a file in the current directory.

• $File::Find::dir is the current directory name,
• $_ is the current filename within that directory
• $File::Find::name is the complete pathname to the file.

my $limit = 20;

find (\&CheckFile, "/Users/admin/Documents/ScriptTest/");

sub CheckFile {
   my $age = -M $File::Find::name;

   if (  -f $File::Find::name
      && !/^\./
      && $age > $limit
   ) {
      rename ( "$File::Find::dir/$_", "$File::Find::dir/.$_")
         or die "rename failed: $!";
   }

   else {
      print $File::Find::name;
      print " is a youthfull ", int($age)," days old\n";
   }
}
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