Current beliefs as to why people age

Throughout our lives all of our bodily systems have cells that duplicate themselves. After a certain number of years, these cells begin to start dying off, or become more prone to mutations that occur in the cell replication process. An example is the eventual death of muscle cells that lead to reduced muscle tone and strength in the elderly. Concerning mutations in cell replication, the more times something happens the more chances there are that something can go wrong. If a cell has replicated itself twenty times, there has been little opportunity for something to go wrong, but when cells have replicated hundreds or thousands of times, pure odds mean the chances are greater for "mistakes". These mutations are what leads to certain diseases that are more greatly associated with aging, such as certain cancers.