Kill Bill star David Carradine has found the secret to eternal youth - younger women.The 71-year-old movie star insists he's in the shape of his life and it has everything to do with the fact his fifth wife is 24 years younger than him.He explains, "Women are at the top of the list with what keeps me alive and young, and I don't hang around with old people. Everybody that I know is at least 10 or 20 years younger than I am. My wife Annie is 24 years younger than I am."My oldest daughter once said, 'Dad, how come you don't hang around with women your own age?' and I said, 'Listen, women my age are usually a lot older than me!'"Part of the secret to staying young is don't hang around with people your own age because you'll get old with them. Hang out with the young people and you'll stay young."I discovered that life begins at 60. The reason is, by the time you get to be 60, you just don't care what happens. You've done it all and you suddenly feel free about everything."And Carradine insists kung fu and organic food also have a lot to do with his good health: "I think kung fu has something to with it and I do all the holistic medicines and herbs. I eat organically and take a lot of vitamins."