Youth is not a period of life. It is a state of mind. It is not a matter of rosy cheeks， red lips and supple knees. It is a matter of the will， a quality of the imagination， vigor of emotions. It is the freshness of the deep springs of life.
Youth means a predominance of courage over timidity of the appetite， for adventure over the love of ease. This often exists in a man of 60 more than a boy of 20. Nobody grows old merely by a number of years. We grow old by deserting our ideals.
When the aerials are down， and your spirit is covered with shows of cynicism and ice of pessimism， then you are old， even at 20， but as long as your aerials are up， to catch wavers of optimism， there is hope you may die young at 80.
该文的一个特点是排比、对比用得好：在第一段里就用了两个排比句，使人留下深刻的印象。在全篇都使用了年轻与年老的对比，紧扣主题，很有说服力。另外，最后一段中“snows of cynicism and ice of pessimism”的句式也是很地道的英语，值得一学。