5'9" for all men.
5'9.5" for young men (18-25) on those doctor's height charts.
Exactly! 5'9" doesn't sound right but it is. In modern society we are used to ceilings being 8' or higher in our houses. But for most of history, people have generally had ceilings a little crowded in their houses. We just aren't used to that and so therefore feel cramped and think "Wow, they must have been short!"
That someone who is 5' 6" can stand comfortably in a room and someone who is 6' has to duck does not surprise me in the least. A ceiling of 5' 10" would work fine in many houses, our culture just wouldn't accept it.