I don't remember exactly when my son got it. But one thing is remarkable that my son has clearly understood he could not go to/stay at kitchen when he was 1yr 2/3 month only.
I told him once exaggeratedly: "Fire, it's dangerous, keep away...."(in chinese), he went away immediatly. Then, he won't stay in the kitchen or even stopped him going when I said it again. Most of the time, only if he heard the voice from fire turning on, he waved his hand to show "Don't go to the kitchen, fire is on now" whenever he was playing in the house.