I suggest reading
The Calculus Trap, an article on the subject.
My DD13 was in the same situation, and I'm very glad I ran into this article. She's already accelerated, and has a 99.x average in accelerated math. As the article notes, we could probably accelerate her again, and get 99.x in yet another class. This would put her in class with much older kids, still not as smart as she is, and she would run out of classes by Sophomore year.
Instead, she's been studying Number Theory, Game Theory, Probability, etc., through AoPS, CTY, self-study, etc. It's giving her a much richer understanding of multiple branches of mathematics. Competitive math (AMC, Mathcounts, ARML) is actually presenting her with problems she can't solve, and she's learning both to be tenacious in working hard problems, and also how to fail and recover. School math is now just a small, easy part of her math work.
The best advice in the article, for me, was the advice to find somewhere where she's just average. We invest 4+ hours each Sunday traveling to a competitive math league for kids up to 12th grade, including a member of the US Math Olympic team, taught by grad students at last years' Putnam-winning school team.
I believe building a broad solid base is more more important than spiking through the standard curriculum with ease. 2 years ahead is probably fine, but I wouldn't go futher. We just happened to stumble onto the ARML team - you may need to search. At a younger age, Beast and AoPS classes may be the best place to start (though our team has kids as young as 10). Even the AoPS standard "pre-algebra" class will go much deeper and richer than a school's pre-algebra class.
