Natural selection is interested primarily in two statistics: attractiveness and boning time. Attractiveness is boring and not the topic of this post so talk about that part of the game with your science teacher. I'm interested in boning time, or maybe just like saying it. The logic goes that the more opportunities an individual has to mate, the more babies it'll have, and the more common will be its genes in the next generation. After a certain amount of generations not very many fish (or jets for that matter) were hanging with the sharks.
As natural selection selects against more and more of a species' skull cracking activities in order to increase net boning time, the life expectancy of the species lengthens as a byproduct.
So assuming that all other factors remain constant, which they don't, the life span of every species on the planet has been getting longer, and will continue to grow as time goes. It'll surely be bizarre when deers live to 400 and redwood trees to 2500. It'll be even weirder when the fish that you got for throwing a dart at a balloon lives for 5 days.
How to live longer? How to increase your life expectancy? Wait a long time.