Genesis 5:9 - Ellicott's Commentary On The Whole Bible

Enos lived ninety years. — This proves that the years could not have been mere revolutions of the moon, as some have supposed. So Cainan was only seventy years of age at the birth of his son, and Mahalaleel sixty-five. In the LXX. no patriarch has a son until he is at least 162 years of age, so that the supposition there would be more tenable.