I noticed that she wore her evening dress, all her dresses, like sports clothes – there was a jauntiness about her movements as if she had first learned to walk upon golf courses on clean, crisp mornings.
A great way to enjoy this sentence is to think of all the worse ways to describe just such a woman. It wouldn’t be enough to just say that she has natural athletic grace. It would be pale cliché to call her a swan, a ballerina, a long tall drink of water. It’s not just that she’s sporty, that she grew up with money, that her cool physicality glows through an evening dress.
She moves “as if she had first learned to walk upon golf courses on clean, crisp mornings.” The magic of this phrase is that it also captures the observer’s social standing, as a man who regards the patrician pastime of golf as a subject of aspiration if not envy. He knows that the only girls who grow up on golf courses are those who have their cares in the world filtered through a fine inheritance.