I want to add that I've gone from sea level to 7600 in Yosemite in a day without any problems and that includes doing some strenuous work on skis pulling a sled. The one time I got sick there was from food poisoning, not altitude, but being that high didn't help things at all. I've skied all day at around 8K with no problems, but I think too much higher might be pushing it. The time I got HAPE, I was 18, so age isn't a factor as far as I can tell.