Does the 95-year-old woman who smokes two packets of cigarettes a day hold the clue? Do blueberries really delay signs of ageing or is it more a question of attitude? Does the real key to controlling how we age lie with a five-year-old boy with an extraordinary ageing disease or with a self-experimenting Harvard professor? For centuries scientists have been attempting to come up with an elixir of youth. Now remarkable discoveries are suggesting that ageing is something flexible that can ultimately be manipulated.