Personally, mind you, this is my opinion based on my own experiences with my children, not based on any scientific study it doesn't make sense to wait until 9 -10 -11-12 months to start solids. My point is that every baby is a little different about when they need to start solids. IMO it makes alot more sense to watch your baby and study the signs. Can baby sit up?...has baby lost the tongue thrust reflex? Does baby show interest in solids? Does baby grab foods off your plate and put them to her mouth? Has baby started "chewing" things...like toys etc. Does baby seem to still need "more" after nursing? (by that I mean that you don't have low supply, baby is older than 6 mos. or so and no matter how much baby nurses, he'd still have room for solid food...with my kids they got to the point where you could see that.)
Every baby is different, and instead of making a choice to wait until xyz months, observing your baby and making the choice based on their particular point in development seems like a better choice to me. You'd hate to miss the mark if your baby actually is ready for solids before 10-11-12 mos. and risk really frustrating baby for no reason.