I coach both boys and girls. hands turned in actually allows you to relieve stress on the elbows. If you have your hands turned out in a handstand, your elbows are more likely to hyper-extend. It's easier to bend your arms should you need to with the fingers pointing at each other. I got this way of teaching it from several college coaches so I've always stuck with it. I've seen the hands being turned out cause elbow injuries that don't ever seem to heal. Some folks don't have the shoulder flexibility to open their shoulders in a handstand with the fingers turned all the way in. I usually just have them turn the slightly in at about a 15 degree angle. I have the same issue with my flexibility. I can't turn my fingers in in a handstand. Many guys turn their hands out and from what I've seen, they don't seem to be as prone to the elbow injuries but I still work on getting them in.