What is a good age to start a 16m for swimming classes?

I started both my babies swimming before their 1st birthday; in both cases I used 'AquaDucks' in Singapore so that they got professional introduction to the water. Got to say, the kids loved it and so did I. It was worth it, just to give me another job I could do with my kids from a very early age, and give Mummy a bit of a break!