We're going to go with PG just because this is a movie about war and death and stuff, but, as was the style at the time, it's pretty tame by today's standards. In fact, until the end, most of the death and mayhem is just implied. For instance, when Kambei disguises himself as a priest to kill that hostage-taking bandit, we don't see any of the actual butchery. The poor dope just comes staggering out of the hut and we cut to a shot of Kambei's blade dripping with blood.
An even more oblique not-violent-but-violent moment comes in the duel between Kyuzo and Designated Opponent. Our man cuts the poor jerk in half, and yet it happens so quickly and subtly that even the dead man himself doesn't seem to realize it.
Part of that comes with the general censorship of the time; the Japanese had their own Censorship Board, created with their new constitution in 1946 to monitor all the awful naughty things that they didn't want showing up in their movies. Hey, we don't like it either, but it was the lay of the land back then, and even Kurosawa had to bow down to it. (It was revised in 1956 because the censors before then consisted of actual filmmakers, which they felt was kind of like the fox guarding the henhouse.)
Hence, Seven Samurai contains very little actual violence, though the director goes out of his way to suggest and convey as much as he can. In fact, some of the film's artistry comes from the sneaky ways he makes it feel more violent than it actually is: conveying the horror and slaughter-happy nature of war without actually rolling up his sleeves and diving into the gore.
But some of it also comes from the nature of war in the Far East, and the way duels were conducted between samurai. Western hand-to-hand combat was very different from what we saw in Japan. Duels often featured knights on horseback, wearing enough armor to build a second Eiffel Tower and riding horses the size of small cottages. The aim was to batter your opponent to death… or just wait until he fell down in the muck and the 250 pounds of pure pig-iron he was wearing pulled him down. Western movie duels tend to follow that lead, with a lot of lengthy drawn-out fights traveling all over the landscape and back.
Japanese swordsmanship, on the other hand, was very different. Instead of pounding the other fighter senseless, a samurai would watch and wait and look for an opening. He didn't need to hit the guy a zillion times; if he did his job, one blow was all it would take… as this movie loves to show us. That also contributed to its weird bloodlessness, and remains a big reason why we're sliding this towards the more kiddie-friendly end of the scale.