Before I answer that, age is the number one issue of the 21st Century. We are getting older! We don't have many kids. The average age is increasing. In country after country, from Asia to Europe, the birth rate has dropped significantly, resulting in fewer people.
Of course, Africa will carry on growing in headcount. But not for long.
The worldwide population in 1950 was 2.5 billion, and 2150 10 billion. Of course, we are getting bigger. But by 2075, it almost peaks at 11 billion, and it stays there for ever. With a population, that is getting older, and older.
In the 70's the number of humans on the planet grew at 2.11% a year. Now, 2015, the growth has halved, and by 2050 it will half again. In short, the population of the world will become progressively older during the coming decades. In 1999, the world’s median age is 26.8 years. In 2025, it is projected to be 35.1 years. By 2050, the median age is projected to reach 43.5 years. Wow. That’s 18 years in 50 years. Almost 40% of people will be older than 50 years.
Look at the data:
According to http://www.geohive.com/earth/world_age.aspx, the population in the 1950s was normal, with the majority under the age of 14 years old. But by 2000, an unusual flattening starts to occur. In 2025 its flattens further, then in 2100 the most unusual change occurs.
If you are older than eighty years of age in 2100, 1 ) you are a part of the biggest age group in the world 2) you are part of 1 Billion people!!
In 2017, over the age of 80 years are under 100 million - and it is is 10x by the end of the century! 1 Billion people over the age of 80!
We are getting much older!
How did we get there? Several reasons, according to Sarah Harper, Professor at Oxford University:
1) As humans develop economically, mortality falls, and sometime later fertility falls.
2) Health care has got better (by far). More people are educated and they have higher paying jobs.
3) Maybe it was the birth control pill. Gregory Goodwin Pincus's birth control pill changed family life, because it allowed couples to do as they please without having to worry about having more children. Women seized control of their family life, and sexual behavior, which changed the way that women and relationships were viewed.
4) Young people want kids, but they don't want them until there they are over 30 years old. One or two children is enough.
5) Nuclear proliferation made people scared of wars. Since the end of WW2, people don't want wars.
I will blog further on these 5 points.
As Sarah Harper says, "Europe, for example, reached maturity at the turn of the millennium, by the measure of more people over 60 than under 15. Asia will hold a large group of working age until the middle of the century. Then its proportion of young people will start to fall, and in Asia there will be more a billion people over 60." She notes Latin American will reach 21% over 60 by 2040.
China is easing the one child policy, at the same time that Chinese parents don't want any more children. The likelihood is drastic for China - China is facing a severe issue of an aging society as its aged population has reached 169 million by the end of 2008, and has been growing at an average rate of 10 million annually since.