The FAA did a study I think in 2012 maybe earlier and found that it didn't matter military, cti, off the street, the only solid evidence they could find that correlated with success is the younger the controller the more likely they would become a CPC. It kind of makes sense and I've seen it where young controllers can adapt better and understand a new set of rules and a new "language" (phraseology) better then someone whose older and set in their ways, obviously not true for everyone.