Win, where in the File::Find::Rule documentation do you see an example of the form
$rule->name(length >= 50);
???
On the other hand, you might try looking (use your browser's 'Find' function, for example) within the File::Find::Rule documentation for the word length, as perhaps there is an example of code which really does something like what you want.

Why do you find it so hard to read documentation? You should know by now that people cannot read documentation for you.