The title pretty much sums it up. Under optimal conditions of light and water and temp., and pretending that there are no herbivores in the area, would plants have a lifespan, or can they die of “old age”?
Well, annuals die every year, that’s why they’re called “annuals”.
Sure. Plants senesce, meaning they grow “old”. But usually its something else that causes them to die (Disease gaining a foothold more than a plant can defend itself or outgrow it). Many palms are monocarpic – meaning they are preprogrammed to die after they flower (this is what happens to most true annuals).
The genus Caryota, the Fishtail Palms are all monocarpic (at least their individual trunks are if a clumper). They usually begin flowering at the top closest to the crown of leaves and send out inflorescences down the trunk. When the lowest inflorescence finally matures its fruit, that trunk dies. For clumpers, a new one will take its place, but the single trunked species, the whole plant dies. The Talipot palm, Corypha umbracullifera is also monocarpic (and has the largest inflorescence int eh world).
Most plants have a finite lifespan; however it may be incredibly long, like a bristlecone pine’s, or relatively brief. “Annuals” don’t always live just one year … here in Hawaii, plants which are considered annuals elsewhere may live for many years, since there is no frost to terminate their cycle. Other plants won’t grow here at all, or won’t bear fruit, for the same reason.
Individual species have average lifespans which can be cut short by accident or disease, or extended by unusually good conditions. Kinda like people. 