I swim every day. I actually think up the best ideas for my articles when I'm touching the bottom of the pool 10 feet underwater. It's good for thinking.
And it's the best possible lifelong exercise you can do. Most people get old and fat at some point. If you're old and fat, exercise is hell on your joints. But not in the water! There's a guy at my gym who swims at lunch sometimes. He had three heart attacks before he started swimming. If he didn't swim, he'd be dead now. He's still got a massive gut and he kind of waddles when he walks, but he moves as gracefully through the water as anyone else.