Regarding verse 17, “…There are four ages within a Great Age, which, when added together, amount to 4,320,000 of our years…”:
It is my thinking that this huge timeframe of 4,320,000 of our years represents the time we each spend coming and going through death and rebirths into Brahmā’s worlds, most of which are less desirable than where we are now. But this is how long it takes to get off the merry-go-round if we do nothing to speed up the process and just go on living ‘normal’ lives.
The four ages within a Great Age define the nature of our circumstances in various incarnations. Of the four ages, there is only one in which beings live harmoniously and are relatively ‘happy’. I don’t know about you, but I would rather go for the gold ring now.