What is the best age to start children for swim classes ? Baby , toddler or preschoolers?

Before 3years old is mainly water confidence .. which u can diy at home or bring bb to the pool yourself It is only after 3 years old that the schools will start teaching strokes I brought my little one for swim trial at mth 6/7/9 the coach commented when my lo was 9 Mths that there wasn't a need to enrol him into one since he has high water confidence .. but just continue with what we have been doing