Good pessimistic question. We think of dying at the slightest failure of love, career,humiliation etc. We encounter the death of danger by our daring activities while travelling, talking, being with friends and loved ones but the question is - do we think that we shall die one day?
The fear of death enters our mind when we are in childhood. As adolescents, we don't think abt death and start doing things out of emotion and fascination (riding a bike, swimming, climbing dangerous heights) When we are young and about to settle in life, we do have more liking for living long and at the same time indulge in risky things with some caution.
So the answer is: by the time we are young, we have full conscious about living long and enjoying life.