@ucbalumus - The focus and concern about math/Calculus BC is because I didn’t think my son is a natural math wiz and sort of surprised that he wants to take Calculus BC so early (though his math teachers are supportive of this advanced path). The other reason is that this is a subject in which he can back off a bit but yet still be advanced, which will allow him to explore advanced classes in other domains, as well as continue his extensive extra-curriculars (competitive soccer and orchestra).
@skieurope - My son seems non-plussed about the potential difficulties of Calculus BC so perhaps all this worrying is for naught. However, it does worry me that this may be a case in which my son need more guidance.
BTW - altough I have tried to encourage hard work and achievement in a general way, we the parents are not helicopter parents, micro-managing and pushing him in any way. The focus on Stanford is also from my son, not the parents. If I had my way, I would like him to attend a small liberal arts college out of the west coast,.