I'm not sure who advocates when children should be off the bottle, but I simply tuned out all the stuff other parents were doing and let my 2 year old daughter lead me on this issue. When she seemed okay with the sippy cup during the day and stopped asking for the bottle during the day, we only offered the bottle at night as part of her getting ready for bed routine, and in the early morning as her first hunger hit (around 4-5 AM) and then she would go back to sleep. Eventually she simply stopped asking for it.
Remember, sucking is a child's most basic instinct and continues on into childhood, even after bottles, pacis and thumbs aren't necessary. It's also a comfort behavior. Stress in your child's life might contribute to them wanting to continue bottles......All in all, don't stress about this. There is plenty of time to wean.
Good luck and have fun!