Well I've been back in training for about 5-5 1/2 months now and my bench has gone up about 85lbs already and I fully expect to have increased by about a total of 125lbs in a year's time.
But, I'm not new to training, just getting back into training which is a big difference, but depending on genetics a person could gain maybe 200lbs in a year, who knows?
There's a guy at my gym of Polynesian decent and he reps 315lbs clean and smooth on the bench at 210lbs bodyweight, cut and yoked. He has been lifting for 1 year and has SICK genetics.