Since the pyramid of wealth is collapsing a lot of people who thought they could retire are having to think about working in the golden years.  Lots of us will be looking for work and Walmart can only hire so many part-time workers.  What will all of the other old people do?  How about jobs in industries that are dangerous if you do them for along time.  Jobs in industries like tobacco, asbestos, semiconductors and lead processing.   Running x-ray machine and cleaning up toxic waste are other examples of jobs that in which long term exposure will have a cumulative negative effect.  If however you start the job at age 65 there are not enough years of exposure left to be dangerous.  Old age diseases like heart or cancer will kill you long before the cumulative effect of working with lead.

So old people can do the cumulative danger jobs, save young people from the exposure danger and make enough money to live for a few more years. A nice example of creative symbiosis.