The problem with your logic is that you think that year zero matters in everyday language. It doesn't. If a child is born on July 17, 1970, I don't think anyone would say the child was born in the sixties. Do you? I will agree that he was born in the 196th decade AD, but that's an odd construct and not one conducive to communication.
yes I do. 1970 was the last year of the 60s. We are not going to agree on this one, I don’t want to argue with a FRiend! :)