It's definitely possible to train dogs to leave the chickens alone; we have done it six times.
I would disagree that younger dogs are easier to train with the chickens, especially with a Pyr. Pyrs are really stubborn as puppies, especially between 11 months to 1.5 years (it can be hell). Our older dogs that we adopted from the humane society have been the easiest to train. The puppies really need to grow out of their puppy play instincts, which can lead to chasing of the birds.
I believe it really comes down to how submissive the dog is to you. If she listens well to your voice commands, you have a fighting chance. It all about having an obedient dog.
Having said all that, I would still recommend a Pyr/Antolian. It may take a lot of patience, but the payoff is worth it. Getting our Pyr was the best thing we ever did. After a year or two without any predator losses, we have complete faith in our Pyr.
Jim