Most likely differences...
1.. Calcium level in soil
2.. Sunlight conditions
All of the big ball roots below and to left of that 20 dollar bill were dug on a east facing bluff (good morning sun) and the soil was just full of lime stone rock pieces (no doubt very high calcium levels). They were all between 6 & 8 years old.
The 4 (much smaller) long necked roots (averaged 22 years old) to the right were dug within 1/4 mile of where those big ball roots were dug. But they were on north facing hillsides in deep shade heavy timber and mostly clay looking soil (no rock, low calcium).
Like that article that classicfur linked to said \"It is not age that makes a ginseng root big\" - It is the growing conditions.
TNhunter