I'm interested about taking up golf. However, I'm nervous... people say it's a physically demanding sport?

I hear from golfers saying that it's really strenuous to walk the length of an 18 hole golf course, about 6000 yards or so. And on top of that one has to shoot a low score with fatigue setting in during the later holes. Do you think these ertions are true? I really want to start playing and develop my game so I can be just as good as the pros.