I don't know, I think a lot of people on this thread are cutting some quality hunting years off by basically tossing in the towel at some arbitrary number.
I think the way you hunt may change, but I just don't see myself hanging up the rifles at 65. My Grandfather, who passed away in September of 2000 at 84, had deer and elk tags in his wallet that he fully intended to fill, and there was a damn good chance of that happening!
Heres a couple pictures of my Grandfather, who filled his whitetail B-tag, and elk tag, the same day on public land...with his model 70 300 win. mag. Not bad for a guy that was just a few months shy of his 80th birthday.
He had a tough time seeing this elk as it was about 230 yards away right at dark on an over-cast cloudy, rainy day. But once he saw it, he rested his rifle against a tree and promptly sent a 180 partition through its shoulders...no problem.
I hunt with 3 guys here in Wyoming that are all 70-79 and they still pack elk on their backs out of designated Wilderness areas. Do they hunt as far back as they used to? No. Do they shy away from some areas they used to hunt? Yes.
A picture of the oldest guy in our Wyoming elk camp...doing what he's always done, filling elk tags and packing them out on his back. Think this guy was ready to toss in the towel at 65? Not hardly.
For the record, once he got to the trailhead, he dropped the heavy pack, but walked another mile back to camp...because it was "such a nice day to be out",,,,