My boys both started at 6 months, although Jack didn't really start eating them until 8 months, and was a fussy eater until about 18 months. He clearly wasn't ready at 6 months and could have gone longer. Tom loved solids from day 1 is a great eater still.

The recommendation for 6 months is based on the fact that most babies' digestive tracts are ready by that age. But some will be ready earlier, and some later. The best way to know is to watch for the signs - losing the tongue-thrust reflux, getting a tooth, AND showing interest (the last one on it's own is not considered enough to show that they are ready, as they want to put everything in their mouth at that age).

Also, they all need more iron etc at different ages, depending on a variety of things including whether they are bf or ff, and how long the cord pulsated for before being clamped (or if it wan't clamped at all). The more cord blood they get the longer their iron stores last. BM doesn't contain as much iron as iron-enriched baby cereals, but it is more readily absorbed, so the baby actually gets more iron from bm than from something like Farex.