In a recent BBC interview, Dame Margaret Drabble - the acclaimed British author, age 69 - said it may be time for her to stop writing fiction - to retire - because her memory isn't what it once was. Her comments have raised some interesting questions about ageing and creativity. Should artists consider a voluntary retirement of sorts? Is there a point when imagination and vitality gives way to repetition, when the work starts to suffer? Are there artists in any genre that you think should retire?