I love swimming. It's great exercise, and pretty good for the joints compared to running. Do you swim for exercise?
It's a pity I don't know how to swim but would love to learn
Really? You know I think it's easier to learn as a kid, for some reason. Fewer mental blocks, maybe.
Ok, What does it take to be a good swimmer?
I would say an ability to stay calm under pressure, mostly. Drowning is pretty scary. 
When did people start swimming?
Not sure in general, but in Sweden for example, the first swim club was founded in 1796!