Thanks Hillhopper.
The oldest in there was planted 7 years ago this fall, and I went back in a couple years after that. Yesterday, I discovered that the patch is now self seeding also, as there are some babies here and there.
I dug a couple roots yesterday to get pictures, and even the huge three prongs are not yet ready to dig for market.
Both of those roots are three prongs and both the same age. The best indicator on size is the thickness of the stem, though that doesn't always predict accurately. That larger root will dry to about a medium size and the smaller one to a small. Neither are big enough to be especially beneficial to a collection of dry roots yet.
These plants were within ten feet of one another, both were three prongs and would be legal to harvest this fall. However, clearly, they need more time to mature before they are going to be ready to harvest.