You can limit movie ratings allowed for watching instantly by setting the maturity level on your account. This blocks watching titles with forbidden ratings, as well as requiring a password when you add DVDs with those ratings to that profile’s Queue.
To set the maturity level: - Go to Your Account. - Under Preferences, click on "Account Profiles" - In the Change column, click on "Edit". - Set the maturity level.
Please note that watching instantly is only available on the main account. Additional profiles will not be able to watch instantly.
... you can open an additional account for yourself if you do not watch instant movies, or set the parental control and change its setting whenever you watch.