shellymos,
About Camp Invention, it might be worth a shot to ask the local camp director if your son could be in the older group. It really is up to the local director. It was a different situation in that the camp director here was my DD's 2nd grade teacher, but last year she let my DD be in the older group since she knew she was ready for the more advanced stuff. Perhaps you could volunteer to provide your local director with letters of recommendation from you son's teachers.
But, I totally agree with what you are saying. I remember being very upset about age restrictions when I was growing up, particularly since virtually all my friends were older than I was. We've run in to that quite a bit with my kids, too. One time it was even the GT director who refused to let my HG DD into a summer camp that was for kids entering the grade that same GT director had just accelerated my DD into. I always ask about an exception to the rule if there is an activity that my DD would like to do, and I explain the age/grade descrepancy, but I'm only successful about half the time.
