''So lithe,' they say. 'So spry and sparkling. So uncannily youthful. How on earth do you do it?' Well, what can I tell you? An hour of tai chi first thing in the morning, an HIIT work-out with my personal trainer, a bowl of steamed kale and a handful of almonds for lunch, and then two hours of yoga in the afternoon followed by an ice bath - this is a routine which I'm sure would work miracles for anyone of any age, although I can't be entirely sure...