That won't help at all, it's just pushing the problem forward. Or what do we do when these immigrants grow old? Import Martians?

The entire demographic crisis is something of a myth. As the number of children have fallen as well, the fraction of the population that is non-productive will remain constant for decades. This becomes even clearer when you observe that as health improves among older people, the retirement age heads upward as well.

And when it actually starts shrinking, well, that'll finally help get rid of youth unemployment.

Peak oil is not an energy crisis. It is a liquid fuel crisis.