sub wanted {
  return unless -f $_;
  my $old_flag = -M $_ > 180 ? 'old' : 'new';
  $ages{$File::Find::dir}{$old_flag}++;
}
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There is certainly a trap of believing variable names.
Like believing the documentation.

This looks like code that was refactored because the
routine name also seems to reflect a time when the author
was going to use a boolean return here and effect his count
elsewhere.

If this was part of a larger body of code...
My first concerns, assuming it does what is wanted, are:

• Is 180 magic?
• Where did %ages come from?
• Are 'old' and 'new' magical, Hash keys can be a difficult call on magicalness.
• Is the routine name okay. Maybe a leading underscore.

The $old_flag might make my list, a meaningless name like
$var seems better. But it is an issue for only two lines.

I would consider inlining:

# untested
if ( -f $file) {
   $age{$File::Find::dir}{ -M $file < 180 ? 'old' : 'new' }++;
}
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