I won't go into the whole philosophy of it in here, but the woman DS and I learn from has her toddlers swimming unaided at 18 months. They prefer to start bubs at 3 months, but we didn't start until nearly 6.

So it can be done, but with the right instruction I think. I don't think it would hurt to take him now, even if you are going to stop for winter. I think there's an age that kids start to fear the water, if they haven't been introduced to it properly, but I can't remember exactly when that is.....2 or 3? Sorry I can't help more.

Anyway, if you're ready to start him now, then I don't think it would hurt at all