There are two primary methods of slowing aging. One is to increase the lifespan. The other is to slow down the process of aging. Longevity is a relative term; if you can live to be 100, it is easy to extend your lifespan. Longevity is defined as the average amount of time a person would live in the natural order of things. For example, the average human lifespan in the USA is 85 years. That's 85 years of living to about 100 years of age. Some people live longer than that, but most people will have to wait longer to achieve their full potential. There are some people who live longer than 100 years. If someone were to live for 100 years, that person would be older than the present age of the Earth, and there would be no humans left. A person is considered to live for approximately 100 years if their average age before death is less than 85 years. (They don't have to be very old, but they must have been in their 20's to have done so). So, the average person lives for roughly 100 years. (I say roughly because of how different people experience life differently. Some people live into their 70's, some into their 80's and some into their 90's).