Want to make it to 100? Just stay trim, not thin, have lots of children and take up hard work at the latter stage of your life, if possible.A recent study has found that the secret of living a long life is not eating too much, but also not eating too little; having more than four children by the age of 30; and working on the land.“This study provides the first estimates of height, body build and other vital characteristics for the future centenarian,” said lead researcher Leonid Gavrilov.In fact, Dr Gavrilov and his wife Natalia, a fellow researcher, at the Centre on Ageing at the Chicago University came to the conclusion after studying the health records of dozens of centenarians to find out why they had lived so long.The husband and wife team analysed the records of 171men born in 1887 who reached the age of 100 and found that all of them had more than four children and were trim as they took up farming at the second half of their life.“Our initial expectation was that thin people would live longer. But it really does not do much, compared with medium body build. There is no need to suffer,” Dr Gavrilov explained.The couple will disclose the details of their findings at a meeting in San Francisco next week.