A twelve-year field study , published in 2003 , found that the Short-beaked Echidna reached sexual maturity between five and 12 years of age , and that the frequency of reproduction varies from once every two years to once every six years . A twelve-year field study , published in 2003 , found that the Short-beaked Echidna reaches sexual maturity between five and twelve years of age , and that the frequency of reproduction varies from once every two years to once every six years .