This article argues that an ageing society has a significant upside.

http://www.newscientist.com/article/mg20627550.100-the-shock-of-the-old-welcome-to-the-elderly-age.html?full=true

The Japanese will soon be the first where 50% of the population are 50 or older. It’s likely that 50% of all the humans who ever reached the age of 65 are alive now. But as we are now finding out an ageing population has more wisdom, more accumulated knowledge and skills, probably consumes less and puts less stress on the environment. Sure, they need more health care but most older people are fit and active, well able to look after themselves. In Europe and the UK less than 5% are in any kind of institutional care.

Imagine that the natural equilibrium for a human population with enough to eat and good health care turns out to be old and stable,  producing only just enough babies to maintain itself! Certainly some of our current concerns, including alcohol-fuelled violence, drug usage and indeed war would diminish greatly if there were simply far less young people around.