DS was a big baby, and I found the comments started when he was about 10 months, people wanted to know when I was going to stop, it obviously made them uncomfortable. After about 14 months I fed DS in private and didn't correct people if they assumed I no longer fed DS.
However, I realise now that it's never going to become socially acceptable and seen as normal (as it actually is!) if we all hide and pretend we don't do it, to humour misinformed people who think it's weird (like some of the posted here, even!) in fact I must admit, prior to being a mother I'd not given it much thought, I thought people fed babies till they were about 1 or so, and that extended feeding was a bit odd. I was misinformed, basically, and had never really thought about it it had my ideas challenged. In the end I fed DS till he was 4 
I remember taking great strength from two other mothers in particular, one who was feeding her 2 year old on a bus, and one who was tslking openly about feeding her 3 year old in the mornings still. Those simple acts inspired me to be more open about feeding my own DC. if I felt uncomfortable I reminded myself there might be a mum around who was emboldened by seeing me BFing in public, and that thought really helped me get over my own feelings of awkwardness.
I now have an 11mo DD, and I'm not going to hide away this time round! i think i may have become a militant BFer
In fact I am quite looking forward to being challenged by people so I can, respectfully and calmly, challenge their assumptions and get them to think about where their negative attitudes to breastfeeding come from.
My own sister, for example, last time said "but you will stop feeding once he starts talking won't you?". IMO, this kind of thinking comes from the idea that the primary function of boobs is sex, and while it's ok for babies who don't understand what they're doing to feed, once they're old enough to be self aware, it's somehow wrong. This kind of thinking needs challenging, if it's ever to be accepted in our culture. In fact the effect of this kind of thinking is actually harmful to mothers and babies, as people give up BFing under pressure from society, and the health benefits to mother and baby are lost.
I don't blame people for thinking this way, we live in a culture which is massively anti-breastfeeding, and if people never see older DCs being fed, and if there are only negative portrayals of extended feeding in the media (fucking Little Britain has a lot to answer for IMO) and if we don't admit to it, how will they ever know it's normal?
So, this time round I am going to BF in public with abandon 
I think I might design a leaflet to give to people who aak me when I'm going to stop, answering the usual questions. The point would be to inform and debunk some common myths and prejudices about extended feeding and challenge their thinking (but absolutely not make anyone feel bad for not choosing to BF!)
Anyone fancy helping me make one?