Um... I know this might be politically incorrect but teaching our little guy NOT to stand in the tub started about 3 months ago. He is 13 months now and knows not to but occasionally tests us to see if we really mean what we say. In short, it's not too early to beginning teaching my LO to obey his parents... this makes for a secure child who knows his boundaries, learns to respect authority and for us, our LO is learning to love and respect his future wife by showing obedience and respect to his mommy.
Hope that helps...