Where I grew up, the town gave swimming lessons at the lake every summer, and just about every kid in town went.
Don't know whether that sort of thing happens anymore - I know that most of the sports stuff we did when I was a kid, has been replaced by video games and skateboard parks.
But I live in an area where many (I first said "most" but I'm not sure if that's true) houses have pools. And there are literally dozens and dozens of swimming schools - and swimming instructors who will come to your house. So most of the kids around here swim, with or without lessons.
Our daughter is 2 - we threw her into the pool last summer to get used to it, and again this year (with the appropriate flotation devices and adult bodyguards) - and she's already doing the "kick and paddle" and "float on my back" stuff. We can't get her out of the pool even when she's shivering and we want to quit
We'll manage to keep her out of the pool tomorrow, but only because we've promised her that we're going to the beach tomorrow - and since we don't have waves or sand in our backyard, she's willing to sacrifice the pool for a day