I don't think this debate will really be settled until we have actual data to deal with, which isn't likely to happen any time soon, because you'd have to observe the same people with, and without MBA's.
I didn't see any commentary on whether someone who is older or has a degree is more likely to succeed in their venture at all. This study couldn't address that question because the survey sample was composed entirely of people who had already reached a certain threshold of success. I find the study interesting mainly because it hints at the answer to this related question, and would love to see some data that addresses this issue more directly.