There's really no reason to begin feeding a baby that nasty rice cereal stuff at 4 months--only outdated doctors recommend it. Babies that are ready for solids should be able to sit up on their own, show an interest in your food, lost the tongue thrust reflex (pushing spoon and food out, that is mother nature's way of protecting them from something their bodies aren't developmentally ready for, so don't shove it in!), baby tries to chew with or without teeth, and the baby is developing that pincer grasp where they use the forefinger and thumb to pick up tiny bits of food--you might notice your baby is doing this when they start to pick up every tiny thing like lint and fuzz and then attempt to eat it!
My baby was doing all of those things (aside from the pincer grasp) at five months, so I made her some baby food to see what she would do. She tried avocado first, and she loved it. She had baby food every now and then (a couple times a week) to get used to eating something other than my milk, and then we started offering her rice puffs. We just give her the rice puffs from the cereal isle, they are a lot healthier than the Gerber kind that have dyes and chemicals, and they are cheaper. She is 8 months old now, and she can pick up all tiny bits of food.
There really is no harm in waiting to feed your baby solids until they are more ready. If he can't eat from the spoon then he probably just isn't ready.
This link has a lot of information and links to other pages with even more info:
http://www.kellymom.com/nutrition/solids/solids-when.html