It's not unusual. My DS was 17 months old when he first slept through. DD is 14.5months and not even looking like she will sleep through. She only has 1 day sleep now - 1.5-2 hours at midday and is in bed for the night at 7.30ish. She gets a bottle overnight as I just can't keep getting up over and over to resettle - I'm too tired. So when she wakes (anywhere from 11 to 4.30am) I change her bum, give her a bottle and then she's back in bed and so am I till 7ish. I know she doesn't need the milk but it means we both get a better sleep and that's all I care about!
Good luck with your little guy, it's hard work having a non-sleeper.