Yeah, started at 5 too. For me it was probably physical. At one
   point I was at a gym - around the age of 30. I was doing really
   great on all the machines and freeweights. I have a naturally
   muscular frame and protein agrees with me so I bulk up easily...
   except.... overhead press. It was the weirdest thing. Whatever
   weight I went to, from the max I could handle down to NOTHING, I
   could only get 7 or 8. Then, nothing. I couldn't do a thing. I'd
   rest for a minute or two and try again. MAYBE I could do 5. Rest
   for a little. Then maybe 3 Then? None at all. Consistent
   pattern. Asked my trainer about it: he mumbled something about
   some extra bone that some people have in the rotator cuff that
   prevents them from being able to do more than a few... but I was
   a little skeptical. To this day, I have nothing else to go on.
   Yet, as a teenager, I won 3rd place in State for my weight class
   for "Clean + Jerk". Same kind of motion. The strength wasn't a
   problem. So, all I can figure is that any length of time holding
   my arms out (or up) at the shoulders was just something I can't
   do. So while in a generic way, perhaps the poker chip thing is
   right for a majority - for me, it just won't happen. I still
   want to know what the heck it is with the shoulders - but
   whatever. Never hindered me. My PTSD over the poker chip thing
   is _probably_ because both that piano teacher + my typing
   teacher later mocked when I said it hurt. Thing is: it did. But
   most teachers teach generically.