"Before drawing conclusions it is wise to examine the (implicit) assumptions. In this case the key assumption is that our economy needs to keep growing and if the existing population becomes less productive (because of age) then we will need to import young workers.
Why does our economy need to keep growing? Because our economic model is based upon a capitalist model of growth. The stock market assumes this as well. Not only do companies have to grow, but if they are to be favored in the market they have to grow at a continually accelerating rate. This is, of course, a mathematical impossibility.
When one of these firms hits a natural limit it is punished by the market.
Why can't we picture an economy which is steady-state and not dependent on growth? We could even consider one which is contracting. As the population ages their need for consumer items diminishes and this goes hand in hand with the decline in the work force.
The inability of economists to look at any other models besides "free market" capitalism is why the world is heading off a cliff.
How about a bit of thinking outside the box?" -- Feinman
Feinman hits the nail on the head. As I have pointed out numerous times the limit of finite natural resources per capita as population increases without bounds is zero. We need new thinking, not just the old economic growth argument which as Feinman points out is a mathematical impossibility. (Comments Lupita?)