My 17 month old still has 9fl oz at night from a bottle. In fairness he only has 9 teeth (late one on that front). We clean his teeth twice a day though. He also won't take milk from a cup at the moment.
I shouldn't worry for now - my neighbour's boy was on a bottle till recently and he's 2 and a half now.
I'm to say that my ds was nearly 3. It was exremely difficult for the first few days and we eventually settled on a special cup but within a few weeks he wouldn't use that. I have just accepted that he won't drink milk and make sure he has plenty of alternatives.
I think they say 1 partly because it's easier to get them established on it before they get to the stage where they won't change and it becomes a big battle. MOst people I know seem to do it at either about 1 or about 3 because anything in between was a nightmare when they tried.
We switched over DS's morning milk into a beaker when he was about 9/10 months, and his bedtime milk into a beaker gradually between 11 and 13 months (tbh it was me hanging onto the bottle not him!) And yeah, just do the usual warm formula at first. Now DS has cows milk dueing the day but I still generally do formula at bedtime, just cos I've been sucked into the whole worrying about how much iron he's getting thing and I figure if he has one formula beaker most days that at least gives him a good start (in case my cooking is particularly woeful that week!) HTH x