Pooperman, this is probably the macroeconomics question that I spend the most time thinking about. I don't have any concrete answers for you, but here are some late-night musings...
EVery single one of the 10 largest economies today is predicted to have a much older population in 35 years. Some, like China and India, will triple the number of 'retirement age' people. Japan is predicted to have
40% of it's population over age 65. Yikes. The US will be getting older, but seems like it will have less of a problem than many other developed nations in this regard. Of course, these are all predictions and it's just a 'best guess' what immigration will look like.
So - from this data here are a few of my predictions
1) we'll see the nature of 'work' change and see a lot more people in their 60s, 70s and even 80s hold down some form of employment. I doubt they will 'work' like we do now - no 9:5 jobs, but we're going to have a lot of people who need to work and not enough young people to do all the work that is needed. Smart employers may anticipate this and create jobs specifically designed for the older citizens. Maybe that means we develop a 'retirement shift' staffed largely by elders that work just on Saturdays and Sundays (allowing those raising families to work the typical M-F while keeping the businesses open during the weekends). I dunno - but I do think whichever companies can tap into this enormous workforce of individuals who both want to work and need to work (because of debt/poor life decisions) will make crush their competitors.
2) Devices for "assisted living" will be incredibly important. In 2050 the elderly will be the Gen Xers - they've grown up with technology and won't be as unfamiliar with it as today's octigenarians are. THey're going to want to continue to be independent even when their bodies start to break down.
3) health care and retirement plans are going to take a massive beating. Health care has always been massively more expensive for the elderly - how will we cope when 25-30% of our population is above age 65? It's easy to imagine scenarios where health care and social security/old age security make up almost an entire country's budget. Will we place more 'caps' on how much health care or SS a person gets if they live too long or get too sick? Ironically, the US is projected to have less problems in this area than others because i's still predicted to have a very large working population.
4) immigration. Here's where I think forecasting models might be way off. When there's a vacuum resources flow to fill it. In this case, certain countries might throw open their borders to young healthy workers. Historically this has happened before, fundamentally changing the ethnicity, even the religion of those countries. It will be interesting to see what happens if millions of people from Africa (for example) flood into China or Japan.
5) we've been really bad at predicting population changes decades into the future. Another world war, a global pandemic like the 1918/1919 inflenza outbreak or the utter collapse (and subsequent exodus) of a very large economy could screw up all of these estimates.
other fun predictions by 2050: India is predicted to have the worlds largest population (1,600MM), surpassing China (#2 with 1,366MM). The US will continue to grow to remain the 3rd most populous nation (398MM), but Nigeria's population could more than double (397MM) leapfroging Indonesia (366MM) to become the 4th most populous nation. Pakistan (344MM) may surpass Brazil to become #5.
Currently there are about 900MM people over age 65. By 2050 there could be over 2B. That's a 130% increase in the number of elderly while our global population only increases about 35%.
A few fun graphs to ponder: