My family didn’t ever censor themselves around the kids, and my mother says my very first word was “shit”, used appropriately when I couldn’t reach a toy. So, yeah, birth. I’m 43 years old now.
I went to the other extreme for a while, and my own children rarely heard such a word from us. When they were very young, we even considered words like butt, stupid, idiot and shut up ‘bad words’ as far as they were concerned. Now that they are teenagers, they give me a lot of shit about that. :p
I don’t think cursing is any more prevalent now, though it might be a smidge more public.