Ah, I guess I can understand if socially he is coming from somewhere where kids were more sheltered. FWIW, my oldest has a bd around the same time and is one year older (turned 13 shortly after the start of this school year). She has only skipped one grade, too, but b/c her bd was right before our K cut, she's a 9th grader. It has been a good thing for her but you're right that academics are just one part of what makes it work or not.
We've also found that getting subject acceleration in anything but math is a challenge. Dd has been able to accelerate some in science by taking two science courses this year. By getting that 10th grade one out of the way, she'll have room to take some other science classes she wants, hopefully. Getting schools to let them just test out, like we had hoped she could do for the 10th grade science course, is hard to come by as well, unfortunately.
I'm wondering, though, whether you've thought about whether it is any better socially to get what you want (math, history, and English at the high school) than to just be in the high school. It sounds like he'd be there for a lot of the day anyway if they could make that happen for him. I'm sorry if I'm pushing, though! Further acceleration really may not be the right thing for him; I'm just thinking out loud.
Kids who need this much advancement are hard to find a fit for!