On what age you will let your kids talk dirty(impolite)?

You know what I’m talking about(sometime we even did that without even realize about it,and don’t expect an example from me). We know that someday soon or later our kids will eventually learn about this harsh language and use it in front of us(or at least we’ll hear them say that somewhere). So,as a parent(not necessarily a good parent) will you let them freely say such thing?,if yes,on what age?. What is your reason?. Did you ever did that when you were a kid?,did you find it acceptable?.