Many thanks to all of you. Lots of interesting things to think about here. I have been reflecting and reading over the last few days. Son could have gone to one of the early entrance college/high school programs, but would have left home 2 years sooner and still finished college at the same young age. We have tried to foster his full development, not just his intellectual dev. His participation at church and sitting and talking at our dinner table for those teen years was very important to us, and he acknowledges the value himself.
I have talked to him now about not doing so much belly-button gazing. As a well-educated adult, he will have most of his interactions with people whose IQs are 110-135 or so. He needs to understand himself but also to understand others and make adjustments.
Good for him he identified the professors as "his kind of people". Right now he just wants to be finished with school and assignments and do "real stuff" - working. But you have given some interesting info for future possible grad school.

Other: I think it is best not to name the college. Son did NOT want a big university. This is a school of about 2,500 students, and his department is quite small. He was determined to attend here, applied early decision.