There can be many different causes of ageing. There are different theories that have been put forward to explain the causes of ageing. One set of theories are clubbed under the banner of DNA damage theories, and these generally state that over one's lifetime, the DNA in the cell gets damaged, and this is what causes ageing. The rate at which damage occurs differs from person to person, and that is what causes ageing to happen at different rates in different people. The different theories under this banner are the DNA damage/repair theory, free radical/oxidation theory, mitochondrial DNA theory, radiation theory.
The other set of theories are clubbed under the banner of built-in breakdown theories. These theories basically state that the process of ageing is inevitable as it is programmed into the genetic code of all living organisms. According to these theories, there is certain code related to ageing that is written into the genome of every organism, which is what makes it inevitable. The different theories under this banner include the disposable soma theory, genetic theory, immunological theory, telomere theory.
The other set of theories are clubbed under the banner of built-in breakdown theories. These theories basically state that the process of ageing is inevitable as it is programmed into the genetic code of all living organisms. According to these theories, there is certain code related to ageing that is written into the genome of every organism, which is what makes it inevitable. The different theories under this banner include the disposable soma theory, genetic theory, immunological theory, telomere theory.