In middle school (Christian) our religious studies teacher told us that ancient Jews used "40 years" as an expression of a generally very long time period. So

In middle school (Christian) our religious studies teacher told us that ancient Jews used "40 years" as an expression of a generally very long time period. So 120 years might be an extension of it, not an actual prediction. I did always find it interesting that it happens to be about right though. But of course it's easy to just record who lived to be the oldest.