I'm not sure why a lot of doctors still say to start with cereals but I've been taught in LLL and my pediatrician that it's best to start with fruits and veggies instead of cereals as they tend to be too harsh on babies system and constipate them. A great book on the subject is Super Baby Food by Ruth Yaron. See
http://www.amazon.com/Super-Baby-Food-Ruth-Yaron/dp/09652...
I fed my first dd about this age and started with cereals and my dd was constipated. I waited a little longer but started with the same cereals for my second dd and she was constipated. For my 3rd, dd, I did more research and paid close attention to her teething and everything- just because a baby grabs for your food doesn't necessarily mean baby is ready to eat food. There are a number of "readiness signs" like sitting up unassisted, doubling birth weight and others.
With my 3rd baby, I didn't feed her until she was about 8 or 9 months, and she was fine. She wasn't hungry at all. When I did feed her I started with bananas and avocado and she has never experienced constipation. In fact, we never did cereal at all. I'd just mash up whatever veggies or fruit I ate and gave her that and she was happy.
Hope that helps!
P.
Christian Unschooling Mom, Author, Birth Doula, Coloratura Soprano