re: What's the point of no return on training a dog to hunt (GSP)

Your main issue will be keeping him under control and reigning him in, if my experiences with late training labradors is indicative of GSPs.

I had a lab we tried to train late who was a powerful swimmer, great retriever (blind doubles from instinct), and just showed awesome instincts. He was a stray we adopted from the neighborhood. Amazingly athletic dog, but we couldn't get him to sit/stay/heel reliably enough for real field work.