Please explain, why do we age?

According to this theory, aging occurs through small and random damaging events in a cell that add up over time. These damaging events may come from our own metabolism, as the basic mechanism of metabolism sometimes causes damage to molecules within our cells.

according to this theory, aging is caused by changes in hormones.

Explanation:

hormones are which are produced by the endocrine system.

"a.) well–developed vascular system."

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."