As a JW there was no difficulty understanding that the earth was billions of years old, or that dinos ruled the earth one time. What did cause some difficulty was the obvious fact that there were carnivores and herbivores. As a 9 year old kid, like most boys that age, I was obsessed with dinosaurs. At that time I didn't know that bible loving crazies actually thought that before the flood no creature ate meat... Riiiiight....
I can't name a single current JW who doesn't believe that the earth is 4.65 billion yrs old or that the dinosaurs went extinct 65m years ago. It's unfortunate, though that the science that proves the human race evolved more than 6k years ago or that the flood never happened is just ignored by the average JW. If it disagrees with the GB's current opinion then it's automatically wrong.
So sad