What is tai chi's value for older martial artists?

The external martial arts — karate, judo, tae kwon do or boxing—are mostly a young person’s game, because they are hard on the joints and spine. It is extremely common for top-level external martial arts masters and senior practitioners in China, and even in Japan, to take up tai chi after they pass the age of 50. Doing a tai chi form is a practical way to extend their physical skills many years past the point at which these abilities would naturally decline in their own martial art. As well as maintaining health, tai chi keeps the hips oiled and moving with speed and power, which lies at the heart of virtually all martial arts.