In the creation of man, after a period of weakness Allah Ta‘ala brings about strength and might. He progresses gradually and is developed physically and intellectually. Between the age of 35 to 40, you reach your peak and after the age of 40 you begin to decline, but man does not look at his beginning and end. We will make excuses for this decline e.g. sickness etc., but it is a reality that we all have to face. At the time of the height of his power, man forgets Allah Ta‘ala, little does he realise that the period of his power is very short before his decline.
Source: Al-Haadi