I looked this up a while back it appears that approximately 15% of us are over six feet tall. The remaining studies have shown that the average male height in the U.S. is either 5'9" or 5'10" depending upon which research you choose to go by. Hopefully that answered your question.
I think it depends a lot on the age group. The overall average is around 5'10" but that's for all adult males, including guys who are your father's and grandfather's age - and I don't know anyone who's shorter than their father, so I suspect 6'0" is probably very average for a 20-30 year old male.