K.
I think the gate and childproof room is the right approach. It will take some time, and you need to be VERY consistent and firm about it, but he will learn. My son - if we're having a "battle" about it (like if he wakes up at 5:00 AM and doesn't believe me that it's still night time) will occasionally fall asleep on the floor by the gate. It's not the end of the world, and it only rarely happens. 16 months is on the early side but not too early, I think. Good luck!