COcheesehead
Give me a museum and I'll fill it. (Picasso) Give me a forum ...
It's an indication, but not a very strong one. As an anecdote: I've never had issues up to 13k ft or so, yet at 14k on mount Kenya had rather heavy headaches - not fun.
Other time I went up to 18k (highest I ever got, in Nepal), no altitude sickness to speak of. It's quite unpredictable.
I would agree with your assessment. I live in Colorado and have zero issues with altitude...until about 13,000 feet. The headache sets in, appetite goes south. It is even worse for my wife. It hits her at about 12,000 feet.