My French is only what I learned in high school, but what I recall being taught (way back in the late 70s) is that although technically tu is acceptable when addressing someone younger and when speaking with close friends, in practice, vous is almost always used; tu tends to be reserved for, say, small children and pets. So it's like a 90-10 mix of vous and tu--or at least, it used to be.

This is in contrast to South American Spanish, in which there's more like a 50-50 mix of Usted and tu. Also, in SA Spanish, Usted is used in intimate relationships, as a sign of both love and respect, e.g., between spouses and between children and parents (even though the children are, obviously, younger than their parents).

Can't comment on the frequency or etiquette of use of "vosotros" in Spain or Argentina. People in Chile told me they had to learn vosotros in school in case they ever had to talk to someone from either of those countries--or, I suppose, to read Don Quixote.