Jasp, the reason for the recommendation being changed to 6 months (yep, the current recommendation is 6 months) is because no solids are needed before 6 months, and introducing solids before their digestive systems are ready does do damage. Some babies are ready between 4 and 6 months, but because there is no easy way to know which are ready before 6 months and which aren't, the safest thing is to make the recommendation 6 months. If they are ready earlier there is no harm in waiting.

HTH.