Doug, you are correct my friend! Age does affect hardiness. Me? I'm in Charlotte and have many varieties in the ground and many variteites in 22g SWps. About 7 years ago, I planted 60+ trees in the ground. They were around 2 years old and grew fine. That same year, I wrapped each tree with burlap and stuffed them with leaves. It was a mild winter and when Spring came I had one amazing crop of figs from Atreano, Improved Celeste, Papa Jon, LSU Everbearing, Celeste, Hardy Chicago, Black Mission, Strawberry, I258, Texas Everbearing, VdB, RdB, LSU Tiger, Alma, Pananas Purple, Katheleen Black, Hunt, Italian Honey, Petite Negra, Smith, Black Celeste, GM-9, Emerald Strawberry, Black Maderia, Black Ischia, etc! The trees grew taller than 6 feet. Five years later, the 5 degree winters came and it took a toll on my trees. I had stopped wrapping them and that winter most of my trees died but came back slowly. The next winter, the same thing happened.
Today, all trees came back execpt, Tacoma Violet, Desert King, Deanna, Alma, LSU Tiger, Black Mission, Hunt, and Emerald Strawberry. Come Spring I will be placing a different variety in these positions in my yard but age of a tree does make a difference. My RdB was one of my oldest trees. It took a big hit and was almost dead. This year I need to wrap it and keep my fingers crossed but this tree is thicker than my knee at the base! A heavy dose of fertilizer brought it back though.