I did it. I dropped out of high school at 16 and took my GED. I went directly to college, and received my diploma at 20. There were a lot of kids doing that when the GED first came out.
However, they closed that loophole now. You are no longer allowed to take the GED until your 18.
It’s possible he had a GED. But if you look at the timeline between when he left school and started college, it just didn’t seem like there was enough time to study for a GED. Maybe he just took it cold without really preparing for it.