@davewill: Remember that there are road builders, and plumbers, and factory workers, and car assemblers and so on.

I know I don't want to be climbing on someones roof to replace their tiles at age 75, or stacking shelves at Tesco, risking falling at that age. If you work in a Bank you may want to continue on and on, but for a lot of people (that are the most physically strained due to their occupation) they cannot go on and on nor should they have to.