We started at 6 months. Best money spent on him. For a long time him and his friends were in a special group as they were all too young to advance up a group but too advanced to stay where they were.
You really notice the difference between the kids who have been doing it for a while and the ones who have started older. The downside is that they can be a little over confident and have no fear of the water.
Ds did have ear infections but his friends didn''t. I think its just his genetics.