At one's peak
A person at his/her peak has reached the highest level of his/her capability. An athlete may feel he /she at his/her peak at a certain time of the day or after a certain amount of exercise. Someone else may think he is at his peak when he is well-rested. The same term can define someone who has attained the highest level of his/her individual achievement in life。“My grandfather decided to retire once he felt he was no longer at his peak。”
Peak是山峰。“At one‘s peak“比喻人在某方面得才能或成就已经登峰造极。对于一个运动员来说，一天的某个时间或经过一定训练后，他/她处于最佳状态。一个人如果休息的很好，可以认为他的精神状态处于颠峰。这个短语也可以比喻一个人一生中最辉煌的阶段。例如：”祖父觉得自己的颠峰时刻已过，便决定退休！