While the statement reads this way, and should be rewritten - the OPs underlying point is that as time goes by it becomes progressively less likely that a 6 month/2 year/5 year/10 year relationship has a distinct meaning for your partner or you. From the folks who are 70+ in the dating pool - this trend has reached the point that they simply don't want to take the time on a relationship even if they are in good health (particularly as bad times are around the corner).

This is more about overall life experience than number of partners. I wouldn't be surprised if its just a reflection of people's understanding of their own mortality which emerges sometime around the mid-30s/40s.