If man compares all desires and pleasures of this life to his age, he will find that the latter is more precious. He will also discover that nothing at all can come to the value of his age, since the pleasures of this world can be regained, while the lifetime cannot be elongated or extended to a single moment:
“All people can only live for an appointed time. When their term ends, they will not remain (alive) even for a single hour, nor will they die before the appointed time. (7:34)"
Likewise, it is impossible to regain the time that passes away in any way, including the possession of all the worldly pleasures. Because he is inattentive to his invaluable lifetime, man wastes his age uselessly, ignoring opportunities. For this reason, the Ahl ul-Bayt (A.S) provided a great deal of instructions dealing with the importance of seizing the opportunities of life.
The Prophet (PBUH) said: “Abu Tharr, You must be stingy with regard to your lifetime, not with your dirhams and dinars (i.e. money)." (1)
“Exploit four things before the falling of four: exploit your youth before the falling of your old age, exploit your health before the coming of your illness, exploit your richness before the falling of your poverty, and exploit your lifetime before the coming of your death." (2)
Amir ul-Mu'minin (A.S) said: “This world is only three days: one passed away with all its insides, the second is that you are living in; therefore, you should seize its opportunities, and the third is a day that you do not know whether you will catch it or not. The day that passed must be regarded as wise educator. The day that you are living in must be regarded as a departing friend. Regarding tomorrow, you have nothing of it except hope."
“Every new day that comes upon man says to him: I am a new day and I will witness you. Hence, you should say only good wording and do only good deeds so that I will testify for your good on the Day of Resurrection, for you will not see me ever again." (3)

Notes:
1. Quoted from al-Wafi; Part: The Prophet’s commandment for Abu Tharr.
2. Quoted from Bihar ul-Anwar; 15/2/165 (as quoted from as-Saduq’s Kemal ud-Din).
3. Quoted from al-Wafi; part 3 page 63 (as quoted from al-Faqih).