I fed mine until they were 3.5 yrs and had no real lift support, just negative comments or sighs and tuts, from family and 'friends'. I don't regret continuing to feed. I do wish I'd been thicker skinned about it and had a few better replies ready, rather than letting them make me feel isolated and slightly inadequate.
I was so relieved that we were still feeding when ds2, at 24 months, was he was seriously ill in hospital for a month. The only food he would take was breastmilk, and we fed and fed and fed! The hospital were great - though at that stage I would have fought off tigers to keep on feeding him, as it was so obviously what he needed, for comfort as well as for nutrition.
"Yes I know people who have fed for a lot longer than 21 months" is a good simple reply to have up your sleeve - you do know us, via MN.
"Most extended feeders naturally self wean at around 4 years" said confidently, with head held high, is also a useful fact to have ready.
I also read a lovely story of a US marine, who was in the peacekeeping forces sent to Serbia in the 80s. He had been breastfed until 5 and co-slept with him mum until he was 7, as both he and his mum made a point of telling all those people who said that she was pampering him/spoiling him, as he passed out as a marine. I seem to recall that he also attended breast feeding support groups, talking to local mothers, whilst he was on active duty!!