I can swim and actually taught swimming for seven years. My brother and sister and I all learned very early. We were all able and allowed to jump off the diving board into the deep end with no floatation devices or parents to catch us at 14 months (mum was on the side, though, if there had been a problem she was within reach). One of my earliest memories is getting too tired to dog paddle to the side and my mom insisting I roll on my back, float until I was rested, and kick to the side instead of her pulling me there because she said I couldn't count on someone always being there to do the swimming for me when I got tired. My mom's younger sister drowned when they were in their teens and so she feels it's very important that children a) know how to swim without aids (so they don't depend on them) and b) know their own limits.
My brother used to LOVE to jump off the diving board, dog paddle to the ladder, climb out, walk to the diving board, jump off, dog paddle to the ladder, climb out, and repeat over and over for as long as he could when he was a toddler. My grandma and her sisters used to think it was hilarious to watch him "run the circuit".
On at least two separate occasions, some uninformed but well-intentioned person jumped in, fully clothed, to "save" him because they assumed he couldn't swim
- he was always small for his age and this was all before he was two, so we couldn't blame them.