Mammals have fuck all in terms of adaptability tactics. Only way for us to adapt, is mix our genes and hope it suffices. The only way we can do that, is reproduction (funghi are op). Now that means more of us in a system that has limited resources (called carrying capacity). We die in order to prevent competing with our children.
This is the reason animals have different lifespans depending on how likely they are to survive in nature. Take a rat and north american opossum for example. Far apart in terms of evolution and size, but have roughly the same life expectancy due to predation. Wolves can technically live up to 17 years, but become fertile at a very young age because the average lifespan in the wild is 5 years due to disease.
It is also the reason menopause exists. It is rare, and found in elephnts and orca’s (both matriarchial species) and humans. This is because the life experience of the matriarch is too valuable. To be able to keep the matriarch around without her being able to compete with her own offspring, infertility is incuded. Post-menopausal orca’s pimp out their youngest sons because it is the best way to pass on genetics they have left. Imagine your mom being your finman.
Humans are the odd one out here since we also have andropause, the male equivalent. A paradox on male reproductive strategy. Which afaik doesn’t exist anywhere else. This is why humans live so long compared to most mammals. Grandparents are important.
Some animals don’t really age. Lobsters simply die from growing too big and unable to get enough oxygen. Some species of octopi stop eating after mating all the way to starving to death. Some animals mate until they die from exhaustion. The immortal jellyfish pretty much recycles itself. And bot just animals need death for renewal. New zealand has a forest which reproduces only after a forest fire. Which happen rarely over hundreds of years due to being in a region with lots of heavy rain. The trees themselves are pretty much immortal, and don’t reproduce while living.
Senesence and death are essential for ecosysems and adaptation of life. Regardless of whether or not keeping an aging body alive is hard or possible.
We age because our cells “choose” to. We have the equipment to live on “forever.” It’s just not our meta.