I spend a lot of time thinking about this too. I'm in somewhat a similar situation and I enjoy math a lot so I like teaching my son before the schoolbus arrives for 10 minutes or so most mornings. Since I started doing so this year this has resulted in widening what was a 3 year gap into a 4-5 year one.
While I don't disagree that mastering Calculus etc. are necessary prerequisites to the STEM disciplines I'm not certain if finishing them a few years earlier will be beneficial or not. For instance, if his interests lie elsewhere then it doesn't really matter how quickly the progression goes, or if its not logistically possible to get access to more science or math while still in high school. I also worry about burn out or superficial mastery.
On the other hand, as my neighbor points out why not learn at the pace you're really at and being bored and becoming disinterested in the subject because the material is not advanced enough is a worry as well.
So I continue on, monitor his enthusiasm and progress and fret a little bit to preserve more options in the future.
