He didn't make Group 1/Group 2 requirements to the Astronaut Corps because he wasn't a college graduate. This was at a different time when not all officers had a 4-year college degree. He could have gotten a degree, if he really wanted to be an astronaut.

During the late 50s, the designers had the plan that the capsule would be flown automatically, and this could have turned off Gen. Yeager from applying, despite his distinguished record.