As far as this "One good thing about the format is that there's very little in the way of clues to student age," is the point just that it's possible to never disclose it, or is it encouraged not to disclose it, or doesn't it matter either way? Is there any philosophy behind this "age-anonymity"?

As far as costs I was thinking.
$X0 for a book
$Y00 for an AoPS course
$Z000 for a Math Summer Camp (for 2-5 weeks, e.g. Epsilon, MathPath, MathCamp).
We had a thread on Math Summer Camps
http://giftedissues.davidsongifted..../all/What_elite_math_camps_are_ther.html
The $Z000 price for a Camp takes people aback, but some here have paid it, and others are thinking about it. In that context, $Y00 for an AoPS course seems more reasonable, even though you can get a book for only $X0.

Our DS7 has been taking K12Inc online courses (for free in a virtual school) and he has been going through the math courses like a hot knife through butter. They are okay for basic presentation of material, but the exercises are rudimentary and unchallenging, and I've heard similar complaints about most course options out there. I gather that AoPS is a rare case (unique? anyone know of others for math?) of very challenging courses which we desperately need to prevent all the pitfalls of whizzing through shallow courses, and never meeting real challenge.

I've been convinced that AoPS Intro to Geometry is a good one for DS to take (eventually, when the time is right), and I could possibly learn a fair bit from it myself, which would not be the case for any other intro or interm course.

We need to pick one or more AoPS courses for DS to take before Intro to Geometry, and before the lack of challenge goes too long. (I'm asking for suggestions.) We have to be selective due to time, cost, potential burnout. Though I could teach any of them myself using just the book, I gather from the review and other comments, that it is worth having the structure, timeline, feedback from non-parent grader/marker, and other potential dialogue.

Out of the following AoPS courses, does anyone have recommendations? And what is a (partial) order of these courses in terms of difficulty, and also considering prerequisites? (DS would meanwhile be taking a standard USA sequence of courses. He's doing K12Inc's PreAlgebra now.)
Algebra 1
Introduction to Counting & Probability
Introduction to Number Theory
Algebra 2
Introduction to Geometry
Algebra 3
Intermediate Counting & Probability
Intermediate Number Theory
MATHCOUNTS/AMC 8 Basics
Advanced MATHCOUNTS/AMC 8

Also does anyone have experience with younger kids (8, 9, 10) handling the live online lessons with the fast reading and typing (with a parent right there to maybe help type)and the fast thinking, of course? Does it work for young ones? How much learning happens in real time during the live lesson, rather than at other times?