I was 21 in 1972 when for the first time a man used the word bull***t in front of me, I had literally no idea, not even an inkling , what it meant, nor had my mother, who was 25 years older than I. This episode took place at an exibition in the Kelvin Hall in Glasgow.
About the same time my 16 year old sister came home from school ( a private all girls' school) and asked Mummy what f* meant.
Again, Mummy did not know, and Daddy asked where on earth my sister had heard that word. When she truthfully replied that one of the girls at school had used it, he wrote a letter of complaint to the headmistress, who wrote back saying that she had no control over the language that pupils heard in their homes, or used during break where no teacher was present.
So even then standards differed. Expletives such as damn, hell were used in my family (by adults) anything blasphemous or sexual was not.
When I was five, I asked my mother how old you had to be to say, "Shut up!" an expression that children were not allowed to use, but that we heard our fathers and uncles say. Amazed Mummy asked what I meant, and I said that you had to be 16 to drink beer or smoke, or drive a car, so how old did one need to be to say words like shut up, damn, hell, etc.
After that incident the grown -ups' language was more restrained for quite some time.