My preflight class (38-58) was mostly prior enlisted, so the shrinks at P'cola used us every Friday afternoon as guinea pigs to take prototype aptitude tests, some of us got electroencephalograms, others shut up in isolation rooms, etc. We were able to ask them questions though, so one guy asked why 26 was the cut off age for flight training since Mother Navy never does anything by odd-ball numbers. They said that if one hadn't made his first carrier landing by his 27th birthday, he'd never make one. They said that's the age when you figure out that you can be killed. Once you've made one and get away with it you'll continue.