So... we can create pristine new life with biological clock reset at 0, but not do so for our own bodies.
Thats the best mechanism nature have to make sure we are evolving - more precisely mixing genes.
What people forget is that our enemies are constantly evolving and trying to kill us, bacteria, viruses, fungi etc. Passing on you dna and eventually dying frees up resources for your offspring to do the same, creating new combination of genes increasing odds of more optimal defense for current threats.
If lions didn't age. They would compete for same patch of land and given all are at the peak of their development roughly 50% of old genes would win resources. Slowing down gene mixing and genetic diversity.
Actually speaking of big cats. Look up cheetah and what happens when you don't mix genes often enough (for natural or unnatural reason)
"Cheetahs retain only 0.1–4% of overall genetic variation seen in most living species, much lower than other well-known examples of genetic impoverishment including"