This is entirely true. On a basic level; the assumption that humans will nearly always be in relationships (and often exclusive ones); will lead one to conclude that the opportunity will potentially be gone. I wouldn't be relying on that option coming up; but it is definitely a thing that can happen.

On two levels:

1. You broke up for a reason, that will always be there (unless it changes - as in 2)
2. I have one anec-data of a guy who is now in his 60s; and reconnected with his first ex-wife, to find they very much like each other; and age has matured the both of them. They now enjoy each other's company in an entirely different way to before. (of course this is looking at relationships from a companionship level not a children producing and biological level)

I tried to simplify and skip points like this but this is a notable point. I did mention poly briefly, but knowing how badly it can mess with the basic assumptions means it would need its own post to cover it.