There's more information on this here:
http://www.abc.net.au/rn/backgroundb...08/2226031.htm

In particular
"At the Royal Children's Hospital in Melbourne, Dr Mimi Tang's been looking closely at these amazing few months of early life.

Mimi Tang: Importantly, some emerging data suggests that there might be a window of opportunity between four and seven months when you're actually very good at developing tolerance to foods. So your natural body's tendency is when you eat a food to not react to it. You learn not to react to it, you learn to be tolerant of it. And it seems that there is a window period between age four to seven months where foods introduced at that time, particularly if under the cover of breastfeeding, you are very likely to be able to be tolerant to it. It's the optimal time to develop tolerance against foods."