Imagine an island with 1,000 senior citizens, each with an annual helicopter-drop income of $25,000. Absent trade links, the money is useless and they have nothing to buy until some of them start working to provide things to their contemporaries. Some large fraction of the senior citizens is just not gonna want to work for money, preferring hobbies and relaxation. In this situation, there is an excess of purchasing power and a dearth of real goods.
But if that island consists of 1,000 healthy 25 year-olds, it's not hard to imagine that very soon there will be a thriving economy as each of them starts working and making stuff to occupy their time and get some of everyone else's purchasing power. In fact, the 20-something island probably doesn't even need the helicopter drop at all. Given some starting distribution of money, it will very quickly flow through their little society.
Today the ratio of old people to young people is really skewed in many industrialized countries. I wonder if the baby boomers all dying will resolve the issue, or whether it will become permanent as each generation has fewer children than their parents did.

http://www.statcan.gc.ca/pub/91-003-x/2 ... 97-eng.htm (Canada, but probably the same in the USA)
People living in advanced countries just don't have a lot of babies.