six months :LOL no i'm KIDDING!!
seriously... around 4. my son is almost 4 and i can't imagine nursing a kid any more mature than he is. already he's showing awareness of sexuality and his own gender identity, and i personally think that's when breastfeeding should be cut off.
eta ~ ... and of course every kid is different. so that 4 years old for my son might be more like 5, or 3, in others.
Gidget, what if the child chooses to wean before then? would you go along with child-led weaning, or force the child to keep nursing until 2 years old?