With our first, the doc said 4 months, we made it three until breast milk just wasn't cutting it. My wife was making enough, but a bellyful of milk just didn't hold her over for very long.
For the second, the doc said 6 months and we said yeah, whatever doc. She was eating table food by six months, having little use for baby food.
Every one is different and it is best to give them what works, not what some committee of academics pulls out of their posteriors.
And when the gov't enforces what the academics pull, what then???
I couldn't have said it any better.
I breastfed my oldest for roughly 6 months, not exclusively. He had lots of trouble with allergies, sensitivity, ear infections, etc. Because of the allergies, in particular, I chose to breastfeed my second child exclusively for 6 months (allergies are very common in both my husband's and my family ).
My second child is now 6, and is just now showing signs of spring allergies. He had his first ear infection at 2, and that was the first sick visit of his life.
I don't KNOW that breastfeeding had anything to do with it. I would recommend it for people with strong history of allergy. It certainly won't hurt, and it might help.