File::Find automatically chdirs into the different directories, so your routine simplifies to

sub TEST_FOR_AGE {
    print "$File::Find::name\n";

    if (-f && (-M _ >= 30)) {
        print FOO "$File::Find::name\n";
    }
}
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It's also helpful that the filetest operators default to $_ and that the special filehandle _ can be used to save a system call. This works fine also for directory names with spaces in them.

-- Hofmator