Dr Mom
Somewhere between 4 to 6 months, babies usually start reaching for your food and wanting something a little more solid to eat. If he is waking up several times a night to nurse - this can be a good indication he is ready for a little more substance in his tummy before he goes to sleep.
Many people have found that by adding a little rice cereal to their bottles, they can help their child feel more full and sleep longer. However, if you are breast-feeding, this is not an easy option. Fruit is the easiest substance for a baby to digest, so that is where I start. You can take organic apples or bananas and blend them up to make a nice first food. When introducing new foods, make sure you give one food at a time for 3 or 4 days, so you can tell if there is going to be any kind of reaction to it.
As you study different opinions, you will find that many disagree with my advice because they claim if you start a child on fruit, they will get used to tasting something sweet, so you will have a difficult time introducing them to vegetables and grains. I have not found this to be true with my children. What I have found, through experience, is that vegetables and grains can be very difficult to digest and so tend to cause colic and tummy aches. They can also be very constipating.
Dr. Christopher taught that a child does not start producing their own digestive juices until the eye teeth and stomach teeth come in (the pointed canine teeth)some where around 18 months of age. Hence, the need for pre-digested food, such as breastmilk. When you use fresh fruits and vegetables during the first year, they come with their own enzymes.