Second, I am a firm believer that using the "months" as a guideline for when to start solids does parents a disservice. First, it provides fodder for other parents to say, "I did this at this age, you should to" or otherwise make a mom feel guilty for starting solids earlier or later than what others say. Babies are so incredibly different...I don't think a mom should be made to feel guilty for starting her DD or DS on solids at 4 or 5 or 6 or X months anymore than someone should try to guilt her for a baby that isn't walking at X months!
The best advice I've read regarding solids is that of looking for the "clues" (i.e., shows interest in what you are doing when eating, reaches for food that you're eating, ~13#, has lost thrust reflex, etc.) that your DS or DD is ready to try them, NOT AAP or pediatrician recommendations.