Charts Bin shows great differences between countries. Canada, much of Europe and Japan have a median age over 40 and most of Africa has a median age under 20. "Median" means half the population is older and half the population is younger than this number. At the link, if you hover over a country, the age by sex will appear too.
How can a country prosper when there are almost no experienced adults around?
How can it prosper when a majority are pensioned off and out of the work force?
The TED lecture by Hans Rosling with animations reveal how rapidly life spans are increasing worldwide. The best talk I have seen. The muslim nations will be turning orange soon.