This movie is a PG-13 in every way. It is rated R in the USA, and 18 in the UK, but it could have been rated PG-13 and 12A.
Infrequently, words like b*tch and b*sterd are said.
There is violence, a man gets brutally beaten up, a man gets wounded at a war and some mildly bloody corpses.
And the usual western violence, such as shootings.
There is use of alcohol, characters frequently drink, but this is quite common in older movies and it's a total know-your-child-thing.
The movie is great, and so is the soundtrack, the director and the actors.
It is not as good as Leones masterpieces "Once upon a Time in America" and "Once upon a Time in the West" (which both are not listed on Common Sense Media for some reasons), but still great!