Andrew Marr celebrates middle age with the scientist David Bainbridge, who dismisses any suggestion of mid-life crisis, to argue that there's much more to middle age than just a period between youth and being old. The poet Simon Armitage asks in 'Knowing what we Know Now', whether we'd choose to live our life backwards once we got to the mid point, but the writer Deborah Moggach suggests there's a gender divide to reaching 50. And the psychologist Claudia Hammond discusses perceptions of time, and explores why we're so obsessed with its passing.