HelpfulGardener.com

they don't live forever with proper care, right? just wondering

The lifespan of a plant will depend on the species, just as it does with animals. Other things that may exert an effect will be the eventual size of the mature plant, changes that take place in the plant that may cause it to become less attractive than one wants it to be, and so on.

Peonies, for instance, like to remain undisturbed, and will grow and bloom beautifully in the same spot for 100 years or more, barring unforeseen difficulties, such as a flood.

OTOH, some of the tropical plants that are commonly grown as annuals in temperate climates can become woody, with sparse foliage and smaller blossoms as they age and mature. That woodiness and other characteristics probably serve some survival purposes when the plants are growing in their natural environment, but they usually aren't considered desirable traits for a decorative plant. That's why the plants are usually replaced each year, even though they might be able to survive if protected from winter temperatures.

Plants are generally divided into three categories:

Annuals. Life span, one year.

Biennials. Life span, two years.

Perennials. Life span, many years. The oldest living plant currently known is a bristlecone pine in the Joshua Forest. This pine has been dendrochronologically dated to be approx. 5,200 years old.

Not all perennials will live so long; life span is genetically determined. But good care will help a plant live out its full destiny.

Cynthia H.
Sunset Zone 17, USDA Zone 9

As above, but as Kisal noted, in the perennial category there are some that are very long lived like the peonies noted and some that even though they are perennials tend to be relatively short lived and die out after a few years. Columbine, viola, delphinium are some e.g.s of short lived perennials. But even though the original plant dies, they often self-seed so you will still have some, just not the same one.