A little before 2.
But really, the terrible 2's and 3's I can handle. It's the f**king fours that get to me. At that point they know better, and it's just the ATTITUDE that gets to me so bad. My oldest improved a lot around 5, and my next will be 5 next month, and he's showing improvement, too.
My 3 year old is two handfuls all by herself, lol, she gets into everything if you leave her alone for a minute, if she's unattended with anything she can color with, I'll probably have artwork on the walls, and she's a major flight risk in public. But I don't know, it's all so innocent yet. There is very little defiant disobedience yet. I know it's coming, though, unfortunately.
Mine are 14 months (twins), and already have more attitude than I know what to do with. Lol they fight, scream at each other, pull hair, clothes, etc. they throw fits, go from one thing to another that they know they're not supposed to have. if this isn't already the terrible twos, God help me. Lol