I think 5 tops. That is when most naturally gain independence anyways it just feels right to me. I stopped at around ten months by choice. No joke. My mom said I would no longer let her. My brothers were about three and four
I breastfed my son and allowed him to wean himself much to the disdain of our pediatrician (we did switch Dr.'s) My son weaned himself at 19 1/2 months and we do indeed have a very strong bond....I would do it all over again!
If I ever have a child, I will certainly let them wean themselves! Breast feeding is necessary for healthy development (imo)... the WHO recommends bfing until two now, I believe.
Also, maybe off topic, but if we as full grown adults drink the nutrients that are meant for baby cows, i see no reason why a consenting older child (okay, breast feeding at 10 or 13 is pretty creepy) shouldn't be able to nurse still. I think 4 is a good age, but let the kid decide.
Sorry, the fact that humans drink so much cow milk weirds me out... always has.