I was about four when I learned how to swim, but I don't 100% remember it (My mom told me the story). I watched my older brother swim in my parent's pool a lot, he did a lot of diving and freestyle moves and I was jealous because I had to wear water-wingies lol.
One day I went to the pool with my brother, ripped off the wingies, and freestyle swam across the pool! My mom yelled at my brother for letting me swim without the wingies, but she got over it when we saw me swimming (rather ungracefully, I'm sure) across a 6' deep pool.
Since then, I've always been a usually strong swimmer =D