Viewer's question?

So I was watching The Doctor's the other day and it was an episode devoted to viewer's questions. The question that intrigued me is probably something all parents have asked themselves. When is it inappropriate to still shower with your child? I thought about that because I admit sometimes it is just quicker to throw Kai in the shower with me then to have to get two separate showers done. However, the experts have said that age 5 should be the cut off point. What do you think??