Lots of districts are actually making 8th grade algebra the "norm" and the advanced kids take it in 7th grade. In fact the NCTM (National Council for Teachers of Mathematics) is having a number of conferences this summer about how to gear the math curriculum in middle and elementary school so that all kids are algebra ready by 8th grade. This implies that it is a growing trend in the nation that it will be the normal course of things soon. So, it really shouldn't be too much of a stretch to them allow younger kids to take it.
My DD took algebra at age 9 with 8th graders and since the teacher had an accepting mindset and understood that there could be social issues between her and the other kids in class she was very well taken care of and accepted. In terms of having kids go to high school for classes early, I would just be sure to talk to the teacher of the math class before it starts and ensure that they are aware of the characteristics of gifted kids (other than the obvious one of being really smart).
I would also be skeptical as to whether or not all of extra math in the summer will be needed. You will probably find that he will need much less time than that to fill in the gaps.
