Rachel,
You've mentioned teeth being a possible indicator of a mature GI tract before. I'm curious about that. Do you have any more information? Both my kids were early teethers (4 & 5 months) and I hate to think of the mess we'd been in if I started solids when they got their first teeth! Colin wasn't ready until closer to 8 months (though we tried at 6) and I haven't started with Claire yet.
Thanks,