W.T.
My 33 month old and 9 month old still nurse.
I would nurse on demand for at least one year and then take his cues. My favorite thing about extended breastfeeding is that in my experience, my kids haven't gotten quite as sick as I or their dad did when we were passing illnesses around. That was worth it's weight in gold for me.
My older son has always had a harder time at night, so that will be the last nursing to go, I am sure. I would think if you were looking to limit nursing after a while, then the morning might be an easier time than the evening.
Do they nurse because they are hungry? As long as they are getting a good amount of nutrition from the breastmilk, then yes.
My older son hasn't nursed due to hunger, I can't imagine, for quite a while. Comfort, security, and of course, all of the good nutrition that breastmilk offers is why he does and should nurse.
Good luck. Keep up the good work!