I stopped at 16 months.
We'd been doing combination feeding from 7 months along with meals so we kind of had set times when we would feed rather than it being totally on demand. We were down to feeding first thing in the morning, before bed and at nighttime if he woke up which was maybe once a night, 2 or 3 times a week.
I cut out the night feeds first by bringing him into my bed if he woke and wouldn't settle, giving lots of snuggles and comfort but not feeding him. I wore high neck t shirts in bed and covered up my breasts with my arm, and told him we had milk in the morning but not at nighttime anymore. It took about a week for him to stop "asking".
Then I cut out the evening feed, again by giving just cuddles before bed and saying he could have his milk in the morning. He would have a cup of cow's milk earlier, too. This took about 5 nights.
Then finally we were down to just the early morning feed and to cut that out I just said, No more milk now in a breezy tone and took him downstairs to start getting breakfast ready. It only took a couple of days and he stopped asking entirely.
It was all a lot easier than I thought, and my periods came back and I felt like I got my body back shortly after stopping, which was why I wanted to stop. DS is 20 months now and has learned to say MILLL in a very plaintive tone when he wants a drink of cow's milk! For me personally I would have found it much harder to stop BFing if he had been frequently using words to ask for a feed like that.
He normally sleeps through now too, although I'm not sure how much that's related to ending breastfeeding.