my girl is 6 months too - she also doesn't like drinking milk!! now she drinks around 18-20oz a day on average, plus 1 meal cereal / congee and 1 meal of fruit...
i think as long as they are healthy, close to 20oz is already ok - plus they should be eating more and more solid food in the next few months...
my girl is eating "sum wing". she's 14lbs 2 weeks ago... doctor said she's a bit thin (becos she doesn't drink too much milk) - but she's very healthy and development is also good (she's growing 2 teeth already) and so there's nothing to worry about.
my girl likes solid food more than milk - she can finish a bowl of cereal (mix together w/ vegetables and fish / chicken) but when it comes to milk, she can only finish 4.5oz max per meal. and very often she's only willing to take 3oz per meal - so she's still eating many meals a day to make up to the 20oz she drinks...