修改以下英文文章：Youth is not a time 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 a vigor of the emotion

Youth is not simply a phase of life, but rather a mindset. It is not defined by physical features such as rosy cheeks, red lips, and supple knees, but rather by one's willpower, imagination, and emotional vitality. Youth is the embodiment of the vibrant energy that comes from the inner depths of life.