Around here (Middle TN) the tallest plants I have ever seen (and have been hunting seng since 1977) were in the 24" tall range. I remember one that may have been a bit taller than that.
I spotted a patch of nice 3 & 4 prongs and as I was about to dig one of the 4's I always break out of the way any brush or vines that may be in the way. I grabbed one of those that I thought was a small sapling and then noticed the leaves and it was actually a big old ginseng plant. Probably the parent plant of that patch.
I did not have anyting to measure it with but I best I can rembmer it may have been up closer to 30" tall. The stem was nearly as big as my pinky finger diameter wise.
The only place I have every seen any 6 footers - was in my dreams