14 1/2 months is on the early side of training so again don't be stressed if it takes a while. I have heard of people that try early, Fail, relax for a while and then try again several months later with success..
Oh , Also be prepared for a few BAD AIM misses with boys.....
Keep a roll of paper towels in the Bathroom and say "It's OK, just try and aim better next time...
When he Starts to use the Big toilet float a piece of Toilet paper in the Bowl before he goes and tell him to Aim and hit the paper only.
Sounds weird, but helps them concentrate instead of just spraying all over the curtains and such...