Besides the very young < 6-7 years old there is no censorship in my household growing up, by the age of 15 it is normal to use vulgarities and cuss. By the age of 16 it gets old and you don't say it because you can but you actually use them appropriately and as embellishments to stories.
I am an Asian and swearing in the house is totally frowned upon. Only my dad is allowed to swear and even then, he doesn't dare swear infront of his dad (my grandad).
No flaming?! Where's the fun in that?
Here goes anyway...
I personally think that there is no harm with using vulgarities amongst children from the age of 5 upward. From that age they begin to develop some sort of reasoning/understanding of actions. As long as the action can be explained and nothing is hidden from the child(ren) there should be no problem. Of course, it will all depend upon the psychological aspects, particularly the attachment type (Ainsworth), between them and their caregivers, but that can just be taken as an extraneous factor.
Haha, I see you read the small text
I don't think children between the age of 5 and (maybe) 10 should be allowed to swear. I doubt most of them that know the swear words do not know the meaning behind them.
Plus, I guess it is morally wrong for someone that young to swear. That's just me I guess.