For instance, a star at least 2 billion years of age is young, a dog at 16 years of age is very old, while a human at 16 years is quite young. A tree can be thousands of years old and still growing, turtles can live up to 200 years.
Scientists like to define aging as a decline in functionality.
That is, we simply do not function as well as we did in previous years. Working Definition of Aging Aging is a continuous process of gradual toss of functionality associated with a chronic inflammatory condition that alters normal genetic control. This is a complex definition, but the aging process is very complex. The body has an enormous capacity to repair the damage inflicted by disease and abuse. These repair processes are under genetic control from the DNA in the nucleus of the cell.