K.M.
My husbands little brother & sister are both lifeguards. My son has been in the water since he was 6 months old. They started working with him when he was 2. & he was in lessons with them @ their city jobs when he was almost 3. Now he is almost 5 & an excellent swimmer. He has been swimming on his own(always supervised) for over a year now. In fact this summer he has been working on his swimming stroke.
I would say now is a good time! Especially if he is going 2 be around water. There was a girl in the class with my son who wouldnt put her face in the water while her mom was around but with the instructor she was doing it, & by the end of lessons was on her way 2 swimming.