Today's 60-year-old cannot be compared with the sexagenarian of our mothers' generation for one reason: phenotypical age, which is the age of the body as opposed to the chronological age of a person.

Last year, researchers at King's College London who examined two groups of endurance cyclists - those aged 55 to 79 and those in their 20s - found these two groups had the same immune systems, strength and muscle mass, and they could not tell participants' ages by looking at the physiology reports but only when they came face to face with them. They followed 125 long-distance cyclists, some now in their 80s, and found they had the immune systems of 20-year-olds. In March last year, Professor Norman Lazarus, 82, who also took part in and co-authored the research, was found to have the immune system of a 20-year-old, thanks to a regimen of regular exercise.