(1) They're more experienced, so lDO the sex will be better.
(2) Cougars will be appreciative that a younger guy will be taking interest in them, and will more than likely make extra sure to ensure that you have a good time.
(3) Hit it and Quit it will more than likely be fine with them, and won't result in any drama that could ensue with a 20 something chick. However, if you do want to pursue something regular, they would probably jump on the opportunity.
(4) 20 something chicks are generally full of themselves (Woman, Woman, and Woman are obvious exceptions), so why deal with all their bullshit, drama, and lies, when you can get consistent sex from a chick who will actually appreciate you.
(5) Cougars may actually pursue you, so you don't have to waste time striking out with chicks at the bar/club. Nothing sexier than a woman who pursues you.