Plants do not age in a sense animals do. It is not completely clear whether they age at all. Vegetative reproduction of plants (natural or artificial) is in a sense an eternal life. And there are individual plants which are thousands years old.

Yes, natural stresses, disease and mutations can eventually weaken progeny derived from vegetative reproduction and they might eventually die off. But there is an escape route for plants - sexual reproduction.

The fundamental difference between runners and trimmings is just that runners are a natural form of vegetative reproduction. Thou, there are plants which will for example drop leaves from wich new plants will sprout. Also it is easy to imagine "trimming" to occur naturally. It will not be obviously the main route of propagation, but it can happen.

Regards.

Vladimir.