@Solve et Coagula,
Well... there are two ways to view these situation. The religious one and the scientifical. First of all i want to state that icome from a strong religious family that devoted to try to guide me threw the catholic way. I know many lethanies and salms from memory. I am no stranger to the religiuous way.
Although on the bible is stated that various individuals lived for a really long time spam, it´s pretty clear that god´s idea of mankind was never inmortaity of the flesh or something related as a millenial life span. Because for him our body is a vessel and a temple that most decay in order to pass to the true life that comes after death, by her side on heaven. And those who sin and do not search for redemption their soul will suffer of the eternal pain of hell.
I really belive in god. But i think he never gamble with dice so he in his sovereign intelligence made these universe with order and laws. That´s what science is about, so heres some scientifical points.
Genetically all the cromosomes of every organism on earth had a gene code on their dna calles Telomers that accumulate during the repetitions of cell divisions. These guide the cells on their age in order to control the times they had divide and if their continue to do so, they seem related with the accunulation of errors in the replication code which are inevitable since life is constantly battling the media.
Technically we live on a oxidative toxic pool. The oxigen we breath and need forcefully for survival forms 21 per cent of the air we breath, and even in that concentration is highly reactive. It destroys complex molecules. We breath a powerfull venom in order to survive and all the organism on earth have a set of mechanisms devoted to the protection of their own structures. The infamous antioxidants.
We are constantly bathing on the suns light which has powerfull ionizing radiation. Our skin is constantly shedding by producing new cells to try to won the battle against mutations and death caused by the sun.
The natural solution to fight these aggresions to organic material was natural selection, those creatures that adapted better to a media were more likely to survive. But in order for them to survive another abrupt change they need to be not completelly equals (not clones). So a genetical variation is always mandatory. How these was achived, god rules instated the creatinon of sexes and the sexual replication. Granting he organisms the hability to constantly combine their genes so the species offspring could have better survival opportunities.
Now there where full grown organisms having an small upbring that will compete for the same amount of food shelter etc... but genetically the offspring was more capable for survival in case of a sudden disaster than the huge parents that had accumulated genetical errors. The logic solution was death. To live we must die because we live in our children.
The resistence to sickness is really variable as are our genes. Some people develop terrible diseases at a yong age, others live more than a 100 years acting terrible with their body. We can not know for sure since parent gnetic mixing is a gamble.
There are records that proof that the life span on early civilization was generally short. There were obvious expections (thanks to genetical variation) of old persons everywhere in the world. But nothing more than 100. And theres no antropologic record of anything more like that.
We can extend our life span by acting as good caretaker of ourselves. For example refined sugars had been proven to accelerate the oxidation of organic molecules on living beens that normally oxigen cause.
Many medications taken daily had proven to lower the likelyhood of serious cardiovascular complications (note i said likelyhood its never a complete certain) That´s why a doctor recommend aspirin to a healthy man over the 40 to 45 years of age.
We live on the golden age of medicine, There are incredible discoveries been made worldwide. There had never been more old persons living at the same point than now. The real problem is to make preventive medicine universal. And medical treatments available for everyone, and i warrantee that you will see 150 year old humans.