By nature we like it or not we will reach an old age…. after the conception,birth, a baby tissues will likely to build up and it is more than tearing up the old tissues….when they grow up, then that’s the time that their old body tissues will tears up….
If we based on the bible aging is caused by the sin of Adan and Eve in which they were cast away in their paradise….
Scientifically speaking it’s the limitations of our body which is genetically disposes by nature…….

Telomere shortening could be one explanation.

Oxidative damage also contributes to aging. Apoptosis, or programmed cell death, is also thought to contribute to aging.

rust never sleeps

Each time cells replicate DNA the chromosomes, which have a long chain of RNA (telomere), they lose a bit of that RNA. The older we are the closer the telomere is to being used up, once that happens, genetic information begins to be lost progressively.