What is the plot of 'Time Enough For Love' by Robert Heinlein?

Lazarus Long, the oldest human alive in the universe, tells his life story to the sentient computer in charge of the planet Secondus. This is done in a series of interconnected short stories, with sections of quotations "From the Notebooks of Lazarus Long" between. Lazarus is thousands of years old, and is ready to die, but his descendants decide to find something to reawaken his interest in life.