My wife and I are both 76 years old and our cabin in Arizona's White Mountains, where we spend May through October every year, is at about 9,000 feet elevation.
When we move up in the spring, we spend the first week doing as little as possible. Even so, we both suffer headaches and fatigue until we have become accustomed to the elevation.
Our biggest problem isn't the elevation, though. It's the shock of coming off the mountain in the fall and returning to our home in Tucson and seeing all the traffic, billboards, buildings and hordes of people.
Bill Quimby