I didn’t learn how to swim until I was like 16. I just wasn’t around water or pools all that often as a kid, and then it took me a few years to get used to the idea once we moved to a house that had a swimming pool. I know several adults that don’t know how to swim, though. Once you know how to do it, it is almost baffling that anyone couldn’t. It’s pretty natural once you realize how it works.