When were the gods of Shintoism born?

The Kojiki and the Nihon shoki, two chronicles written in the early eighth century, depict the ancient myths and history of Japan.
According to the chronicle myths, there existed the first threegods; Amenominakanushi-no-kami, Takamimusubi-no-kami, and Kamimusubi-no-kami were invisible.
Later, a god couple, Izanagi-no-mikoto and Izanami-no-mikoto, produced the eight islands of Japan.
These gods are objects of worship at shrines as symbols of ancestors.
All natural objects and phenomena are also worshipped and considered as having gods, so there are myriads of gods in Shintoism - as the phrase goes, yaoyorozu-no-kami(eight million gods).