Prophet Muhammad says:

…that time ... life spans will grow longer.
(Ibn Hajar Haythami, Al Qawl al-Mukhtasar fi 'alamat al-Mahdi al-Muntazar

In the past when there was no medicine for most deadly diseases, life span was short and people got accustomed to that but amazingly the prophet predicted that life span will not always short and at a certain time the life span will be longer.

Owing to the advancements in medical science, the human life span has increased, long time ago the life span of the humans was short, people died in the past because there were no medicines for most of the diseases, even these diseases were not known.

New medicines were discovered, new technology is being applied especially in surgery, antibiotics have been discovered and brought fruitful results, heart diseases are now cornered owing to the new technology. The human anatomy, a new science, helped so much in understanding the different functions of the human organs and prepared the way to organ transplants.

The science of genetics and the human genome gave a key to the understanding of many hereditary diseases, this has given hope to the rise of life expectancy.

According to the United Nations Department of National Population, over the past few years, the world’s population has continued on its remarkable transition from a high rate of birth and death to one of low birth and death rates. The substance of this transition has been the growth in the number and proportion of older persons. Such a rapid, large and pervasive increase has never been seen in the history of civilization.23

This increase in life expectancy must have a cause. The development of health services due to the advance of medical technology has made such a situation possible. In addition, developments in genetics and the rapidly advancing Human Genome Project are about to incept a totally new era in the field of health. These advances are of a proportion that people living in earlier times could never even have imagined. Based on all these developments, we can say that people living in our time have reached the long and healthy life described in the above hadith.