We've never tried Aleks but since your son is a math kid how about trying AoPS? I am sure he would pass the "are you ready" test and it may provide lots of depth and challenge for him. You could always get the textbook and go through it or at least have him look at it and see what he thinks.
I wouldn't be surprised if he could do Algebra in 5 months. I would still look at AoPS though. He could get more out of it.
BTW I hope a few years from now you will have it all figured out and be able to tell me what's the best thing to do for Algebra LOL
