18 months here too... although she did start up again for about 6 months last September (just over two), but I think that was more due to me driving her round in circles til she passed out so that pregnant me could sleep.
poor wee lad, he is now in bed and it is only 5pm here, lasted all day until dinner time when he broke down sobbing and nodded very meekly when I asked if he was tired, took him to read a story and was asleep about ten seconds later!!! No dinner or anything, I am soooo not ready for this to happen. I would have thought he would cut down time wise for a while or something or start going later but he has gone from 2-3 hr sleeps to none!!!
ds tends to drop them and come back to them. if he is dropping at 5 then it doesn't sound like he's completely ready. the nanny who looks after ds has often gone to naps every other day for a while, she says that can work well. For ds at the moment, if I drive him or pushchair him anywhere at about 2 or 3 o'clock, he'll fall asleep, if not, he won't. Real nightmare period in some ways, but at least an early bedtime is possible if he doens't sleep.