Ratings today are considerably "deflated" from where they were in the '70s, as the G rating has become box-office death and even kid-oriented movies seek PG ratings. There was a time when a PG-rated movie could actually have nudity in it, as in Clash of the Titans
, because at the time it was perceived as an older-skewing rating than it is now. I daresay it was the "deflation" of the PG rating that made it necessary to create the PG-13 rating for edgier films. Indeed, even some G-rated movies had nudity and sexual content back then; to quote TV Tropes
Planet of the Apes was rated G and you saw Charlton Heston's bare butt, not to mention all the violence, "damn dirty ape" and "God damn you all to hell!" The G-rated The Andromeda Strain also had bare butts along with a dead woman's breasts. Sinbad and the Eye of the Tiger was rated G and it showed Jane Seymour naked and almost raped. The John Wayne True Grit has a scene with Dennis Hopper's fingers getting chopped off by a psychopath. Olivia Hussey's nipples didn't block a G rating for Romeo and Juliet.
So at the time, the G rating was seen more as a "family" rating than strictly a "tiny children only" rating -- closer to how we see PG today. After all, the G stands for "general audiences."
As for language, according to the transcript
, there are three occurrences of "hell" (more times than it was used as a profanity in the entirety of TOS) and four of "damn/ed."