[globalise83]

That's very true: the opportunity cost of most business projects is effectively zero once you are retired, so you can pursue something only marginally profitable that you enjoy and it counts as a win. In fact you have a competitive advantage against a 40-year-old with a young family to support.

[MrMcCall]

The corresponding quote to:

  Youth is wasted on the young.

is:

  Wealth is wasted in the hands of the old.