We are not DA parents but recently did the tour. I felt like the one major thing they had to offer over other schools was the understanding of the whole child. They seemed really focused on giving even PG kids a very well rounded experience, rather than just hurrying them through school. I appreciated their desire to keep them as long as possible and not just put a 13 year old in college full-time. In a setting with a bunch of 11-14 year olds all working at very advanced level, they can keep them together instead.
As for being 9 at the academy, I wouldn't want to send my son that early (who is now 7). He might be academically ready but he is not physically or emotionally mature enough to sit through a college class. He would need the academics from a teacher who understands that he still needs to wiggle a little. He simply wouldn't be able to be in a class with 16 and 17 year olds.