There are more than 300 theories of aging. Every aging change is analyzed, by the specialists in the respective domain and transformed in one new theory.
All the Theories of Aging can be reduced to 3 basic theories:
1. Evolutionary Theory of Aging
2. Wear and Tear Theory of Aging (Rate of Living, Free Radicals ... I have to add this one here because the theory is just wrong)
3. Programmed Death Aging Theory
From all the theories Evolution Theory of Aging is the only one which can explain the current life span of species and which can predict different maximum lifespan based on the evolutionary pressure.
Enquiring into the evolution of ageing aims to explain why almost all living things weaken and die with age. Exceptions such as rockfish, turtles, and naked molerat are highly informative.
Evolution Theory of Aging explains why we age, but it does not explain how we age, other theories explain subsegments of the aging process and changes.