Retirement itself is an invention, an innovation, that came about in the late 1800's*. It's reinvention is an example of the life cycle of an innovation, where outside forces ( in this case longevity) create a need for re-invention.
http://www.retirementreinvented.com/
* http://www.nytimes.com/1999/03/21/jobs/the-history-of-retirement-from-early-man-to-aarp.html
