Partly younger guys win because they simply have more hours in the day, more hours in the week, that they are free to play tennis. Many also start a summer having played in the spring on a tennis team. This makes them fit for the task, when it comes to competing in tennis against an older man. Circumstances often force older guys into sedentary roles: managing a desk all day, driving children here and there, doing lawn work. . . at a time when younger guys can work out. There is also a Tedium Factor. Let's face it: once you've played the XYZ Tournament for five or six years, it's just not a very compelling thing to fight for. It's the same old, same old. So older men often value winning less, since it's. . . another game, one of thousands played. Older guys just may not care as much. Younger guys in some instances also can get pumped about beating an older guy; start with confidence that they'll win. And this free confidence can be a valuable thing. (Of course, some younger guys are a bit overawed by playing an older man and expect to lose, the street runs both ways). I think the chief thing in tennis is the drop in physical ability that older guys have because their lifestyles do not permit them to be as physically active. I don't think the actual physical drop-off is that great if an old guy works out.