You have posted about a subject that I am passionate about. I was a math major in college , have a master in statistics, taught college statistics and work professionally as a statistician. I also have a high school aged daughter and I'm very interested & involved in her curriculum.
In my opinion, only children that are truly GIFTED (and I mean "gifted" -- not above average) can master math in the sequence / ages that you are describing for your son. The strong math student should be on a track somewhere split between what YOU experienced and what your son will.
I just don't think kids have the maturity, brain development for Algebra 1 as a 7th grader - some introduction to algebraic concepts, yes, but not the first year of Algebra. Additionally, I don't think a high school junior can master calculus.
I also disagree with the courses that fall into a typical high school math curriculum. Unless you are going to be a science major, math major, engineer, etc, I don't see any use for trigonometry. It has a very limited application. Additionally, I would argue that statistics is a far more valuable class for a high schooler than calculus.
We are bombarded with data in our live every day and statistics is a better "life skill" that offers critical thinking that is more relevant than calculus. Just the concepts of hypothesis testing and confidence intervals are things we see all the time (eg political polling with a +/- 3% error).
I disagree with the previous poster about expectations being lower today. My daughter faces a much more challenging curriculum in high school than I ever did , and I was a good student. She was taking AP classes as a freshman -- I never had a single AP class until I was a senior. I find that crazy.
FWIW, as Cornell notes (at least in our state) there has been an effort in the past few years to push the curriculum 'down' (meaning starting Pre Algebra, Algebra, Geometry, etc) in earlier grades. I agree with Cornell's observation in this area but want to add that something lost in this process has been the ability of a school to ability group students in the 5th, 6th and 7th grade years and offer math to each group at (on) their level. Whereas now you have to get every student along the Pre Algebra, Algebra, Geometry path ASAP (whether they are ready or not in too many cases), previously a good number of schools could offer courses to their 5th, 6th and 7th graders that allowed an approach closer to individual needs (again accomplished by ability grouping).
When I went to school (ages ago to be sure), many aspects of Algebra and Geometry were introduced in our 5th, 6th, and 7th grade years but without the time pressures one will find in the actual Algebra and Geometry courses. It was hard work, but when a class is full with students of similar ability, instruction is much more effective.
I'll continue to respectfully disagree with Cornell about today's expectations though because so many kids have become lost in the process of pushing 'down' the math curriculum (they do not 'get' math) that schools have been forced to utilize more class time (additional periods) for remediation purposes. That, in turn, limits the other courses a student can take (which is not a positive trend) while at the same time a growing segment of students realize they have an 'out' if they just do not want to do the work (and have math courses throughout more of their day).
There is a small segment of our students who do want to consume as much as they can academically (which sounds like a description of Cornell's daughter for sure). As the father to three kids who took many AP courses, I can tell you my pushing of my kids to/toward AP courses ASAP was to avoid the classrooms too full of kids who did not want to be in school (which is another problem entirely, but eviscerates our classroom effectiveness).
Perhaps the fairest conclusion to draw is this: if the school can offer a wide enough array of math courses, a student does have more course choices today then ever before. A segment of students will always choose the most challenging courses - and we need that segment to grow based on merit. But for the majority of students, far too many are choosing the easiest (and laziest) way out of high school and they are less prepared for whatever is next in life than ever before. Subject remediation (common in math, literacy and many of the sciences) makes it easier for students to make less than minimal effort and slide by. That is NOT the type of environment conducive to producing young adults ready to face the challenges ahead in life.