If the human life span is increased by 20 years, what are the problems associated with it? What will be the immediate as well as long time problems associated with the increased life spans of humans? For example, fewer job opportunities, etc.
Life expectancies have been increasing in general over the last 200 years due to an increasing standard of living, at least in the West. As nations around the world industrialize, the birthrate drops and life expectancies increase. This will shift median age higher, but may not necessarily mean an increase in population with all its associated horrors, as the decline in births may counter that. Will it mean fewer jobs? Yes and no. There may be fewer unskilled jobs, but the demand for skilled workers will increase, so these may balance as well. In a few generations, the world may find itself older, wiser, and fewer.
That depends on a lot of things. If people just manage to cling to life longer, there could be greatly increased health care costs. While that would help the economy in some areas such as pharmaceuticals and health care workers, it would overall be costly. If people live longer and also stay healthy, there could be problems in terms of increased numbers of candidates for available jobs, and unemployment increases. We are also talking about a net increase in the population of the planet--an average 20 year increase over the current 70 or so means that there are essentially 20% more people for the planet to support at any one time. Environmentally, this could be a disaster. Socially, there could be some changes--if people have more time, they may spend more of it getting an education, and delay entering the workforce.
I would not like to call it a problem. Let us just call it the impact of increasing life span. Also when we talk of increasing life span we are talking of average life span. Thus we need to differentiate between increase in average human life span by reducing mortality of infants and young people, from increase in life span of people who die at more advanced ages.
The main impact of increasing life span of people beyond their retirement age is percentage of people employed in productive work reduces. Also in general older people have different kinds of needs and preferences, and thus the pattern of consumption by an economy also changes with changes in increased number of elderly people. Elderly people require more medical care facilities.
The impact of reducing infant and child mortality has some hat opposite effect. It reduces the number of people who will be available to take up productive work in future. When a person dies before becoming productive worker, all the investment made by the society in his or her upbringing is lost.