I don't think there is a time or place where marriage is not normative. There have been many where marriage was not practiced, but how many of those societies reached technological, cultural, or philosophical greatness? Could they have done better if they had honored marriage? Even ancient high cultures which had all kinds of other problems like slavery, pedophilia, polygamy, etc held marriage in esteem, at least among the upper classes.

As far as the earliest cultures not practicing it, there's evidence for marriage in ancient Mesopotamia, and quoting from ancient scripture, "Have you not read that He who made them at the beginning made them male and female and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh'?" God made the world with a pattern to be followed, deviate from it at your own risk.