My 13-year-old daughter and I just got back from an attempt on Shasta. We camped the first night at Horse Camp, the second at Lake Helen, and had intended to summit today. However, she was really feeling the altitude starting at about 9000 ft (headaches, shortness of breath), didn't get any sleep at Helen, and wasn't feeling better in the morning, so we decided not to attempt the summit.
It's strange how unpredictable altitude sickness is. In the past I've done several hikes with her at altitudes of up to 12,000 ft, and she never got any altitude sickness -- I was always the one who would feel it more. I think she may have been more susceptible because she had just finished school and had been celebrating by sleeping until noon. Because of a series of recent severe injuries from chunks of ice falling off of Red Banks, we were told to make sure and head for the summit early. I kept gradually getting her up earlier and earlier every day, but waking at 5 still felt pretty extreme to her.
This was still a cool trip. The extreme prominence of Shasta meant that we got incredible views, even from Helen. We took a course in the use of crampons and ice axes, and we both thought that the practice in self-arrest was the most fun part of the trip. This was my first time camping in snow, and I learned a lot of new skills, like snow-anchoring our tents with shopping bags full of snow. Got my 80's-vintage stove to light at 10,000 ft, which was a feat in and of itself.