I wonder if he is already getting canines.
I was gearing up to night wean Juliana around 17 months and then I noticed she was just barely starting to get canines and it was already affecting her sleep a little. I decided to hold off. It wasn't until a few days shy of 20 months when they had completely come through and I finally night weaned.
I was in your situation at 17 months. Now I'm STTN blissfully, until at least 5:30 or 6 when she gets some milk and then back down for a couple more hours.
I wouldn't wait for 2 year molars. Juliana is almost 25 months with no sign of them.