Great job you did with your kids. My grandfather was an educator and my father graduated at 13 as well and went to college. He hated it though because he was too young to meet girls since they were not interested in a 13 year old. But he did become a Dr. Then he joined the military to be in Europe with his father during WWII. But his father was in Germany and my dad was sent to Italy.
As you drive by your local high school, think of the top 5 to 10% of the teens stuck in those centers of ignorance. They, too, could be doing what your dad and my children did.
As for college and socialization, it was a drop them off, wait in the library, and pick up after class situation. It wasn't until they were in their later teens that they began to join in socially with the other students. For socialization they did the usual teen things with their church, dance group, scouting, and homeschooling friends. The oldest was an accomplished athlete and have many good friends with his team.