DC1 self weaned at 3y9m. Lots of aspects of bf him were really hard but I'm so glad he self weaned, it was a very easy and rewarding end to that time. I'd put my own boundaries in prior to that though, at some point I stopped feeding other than bedtime/first thing/naps, then he stopped napping, and later i stopped the first thing feed so by the time he 'self weaned' id already cut it down to just a bedtime feed. It was a dance for two. 
DC2 currently feeding first thing, bedtime, and occasionally during the day (though often I refuse) at 3y3m. I've had a lot of aversion over the past year with her and thought I was going to have to wean (but kept putting it off as I didn't want to stop on a bad day...). The past month I've had some more rest, started taking a calcium/magnesium supplement, and drinking loads of fennel tea, and the aversion has completely gone and I feel more ready to stick with her again. I wouldn't rule out weaning on my terms, I feel like at three years she's had a good run and what I want matters too, but I'd rather let her do it on her terms if I can.
The fb group 'breastfeeding older babies and beyond'(?) is a good place to see all the different sorts of normal.
Final thought - "self weaning" always sounds like one day the child just stops asking, and that's kind of hard to imagine. I know sometimes it genuinely does happen like that, but more often I think it's a change in routine or similar, and you have some control to nudge it in either direction. My DC1 stopped during a bout of mild illness - I think he fell asleep one night early, 'before bedtime', so we missed that feed and then another and kind of got out of the habit. I could have reminded him but I didn't. Then he went back to it for a week or two, and then he really was done, like it had given him the chance to reflect and decide he'd outgrown it. I think the whole process of weaning was filled with opportunities for me to help him miss a feed, or help him remember. The mother isn't entirely helpless IMO.