When to stop breastfeeding?

When do you think is the right age to stop breastfeeding
I personally think 1 year is ideal age and a very max of 2 years old. I think it's disgusting seeing a child who is 3+ feeding because they not even feeding its just a habit at that age. My freind breastfeeds Her 4 year old and he isn't even feeding properly he is just using her nipple as a pull toy in his mouth. I agree breast is best but only Untill a certain age.
 What do you all think?