Here's one to add: if your app has a in-app purchase of more than $100, your app HAS to be rated 18+ because of a fear of teenagers can run up their parents' credit card bills.
It's somewhat unfair because 18+ means adult content, but an app might not contain adult content (as was the case with our client's self-help books/videos).
It could depend on the reviewer, or the app could have been grandfathered in before that policy went into effect? All I know is our client's app got rejected with that as the reason (ours was rated 9+)
It's somewhat unfair because 18+ means adult content, but an app might not contain adult content (as was the case with our client's self-help books/videos).