In the average woods around my house... a wild ginseng plant usually changes from a 2 prong to a small 3 prong in the 5-7 year range. And they usually start producing berries in that 5-7 year range too, but just a few. Sometimes only 2-3 berries which increases slowly over the years until once in the 10+ range and they migh be putting on 8-12 berries then. I have seen them 35-40 years old in this average woods, and still producing a max of 8-12 berries.
Now that is in the average woods around my house (good timber, probably a little too much shade for ideal growth of seng)...
But now when you get down the main hollow to the creek, and go around a bluff that faces the east... there is some huge ginseng that grows there. It is getting ideal light conditions (lots of morning sun) but no hot evening sun, and is growing in mineral rich (limestone rock chip filled) soil.
Below is a pic from a nice wad of berries I got off of a 4 prong on that bluff area... which looked to be in the 7-8 year old range.
Location / growing conditions - definitely make a big difference in berry production as well as how large and health the plant is.
TNhunter