Hey, we started when DS was 6.5 months but stopped shortly after because he was not that interested and got a nasty diaper rash. We just restarted last week and he is now 8 months old and LOVES them. But, we do it in moderation, only after breastfeeding and max of 2x.day. He will usually finish off 1 stage 2 jar of organic bananas in those two feedings.
The little guy I babysit however just turned 5 months land LOVES his rice cereal. It is a hit or miss when he wants it, but on the days that I get it right, he laughs, coos, smacks his lips and pretty much every other baby sound when he sees the spoon coming. But since he is so young I would never push the food. It is something that his mom started him on and I am simply following her requests.