I knew as early as 5 years of age and my son exudes a strong liking for it though I have not discussed it with him. I could see it in him as young as 3 years of age. He acutally continues to exhibit a pretty strong form of play for his age.

I believe it has to do with your perception of sensory. He associates a spank on the but with play since I played with him like that. Just a pat you know, nothing much, but I never spanked him. I believe that lecturing and negotiation are better alternatives because he is smart. But you see that meant he was wired to believe that spank means fun and laughing and mom's in a good mood. Not hit = hurt and I hate it.

That is just what it seems like. Who knows.