I feel that I should point out that the question posed by shinypeople was:
"just out of interest, at what age would most of you think "yuk" to a mum breastfeeding?"
Note the word think. From looking at some of the comments made here, it seems that some people don't feel that other people have the right to have (dissenting) thoughts at all.
So yes, I do think breastfeeding a four year old is an odd thing to do. Notwithstanding any WHO evidence with health benefits all round (which I am happy to acknowledge).
I am not saying that it's morally wrong, or that my opinion has any special validity, but it is none the less my opinion.
Whether or not you have children, toddler, older child or baby, and whether or not you have breastfed or for how long you still have a right to think.
Of course that does mean I would be making a judgement on any woman I might happen to see breastfeeding their four year old. To be quite honest I haven't seen that happen for many years, and who knows what I might actually feel if I did.
We all make judgements all the time, and that's part of being human. I don't think that anyone else can stop that really. Now it's quite reasonable to complain if someone makes their feelings of "yukness" obvious, but otherwise why should it really matter? Each to their own, that is both their own choice of behaviour, and their own choice of feelings.