Hi, I have 5 daughters. With the first one I "went by the book" (back then anyway) and started her on rice cereal at 4 months. The next three were probably around 4 or 5 months. But the last one I soley breastfed and didn't start her on solids until she was a good 6 months.
There is no need to rush into solid foods. People seem to be in such a hrry to do that! Their little tummys aren't made for that real early. It doesn't hurt to wait until 6 months...unless you've really got a baby who is hungry or ready for solids. Babies have that reflex of sticking their tongue out to push things out of their mouth if they need to, when that reflex is gone you can give them solids. Also when they are sitting up well on their own it is time.
That's my "professional" opinion.