Justin Bieber -- 13-Year-Olds Can Handle F-Words

Justin Bieber insists ... 13-year-olds nowadays can handle a few F-words -- which is why it doesn't make sense to give the new "Bully" movie an R-rating ... especially when young teens can benefit from the message behind the film.

Bieber called in to "TMZ Live" moments ago -- claiming the anti-bullying message of the new documentary far outweighs any harm that comes from the F-bombs contained in the movie. As a result, the rating should be lowered to PG-13.