i think it's such an individual thing. some babies have systems that can handle solids on the earlier side, and us mamas, if we're paying attention, can be attuned to the needs of our children. the operative part of that is that we're paying attention, and our instinct and judgement is not clouded by social convention, bad advice, or the pushy nudgings of a nosy mil.
i 'knew' that dd wasn't ready for solids until closer to a year. i did give her chunks of food that she could self-feed (i don't believe in spoon feeding babies) but on a very limited basis, and i gave it to her for fun and exploration. as her mommy, i could just tell that her stomach enzymes and intestines just weren't ready for anything more than occasional tastes of fresh organic fruits and veggies. it's not that she didn't like solids, either...it was just that my inner mama's instinct was telling me that she just wasn't quite ready to be ingesting, digesting and relying on solids for nutrition. perhaps it's something primal that we know from the smell of our child's breath or observing the quality of their bowel movements, but it's certainly not something that i 'learned' from an article that i read online.
now dd is 14 months old and just recently, i'd say in the last 2-3 weeks or so, i've been feeling much more comfortable with offering her most anything. and she loves every morsel of what i give her, whether it's tangerines or grapes or rice or pasta with pesto or grilled salmon. she still derives about 95% of her nutrition from breastmilk, though.