Groucho Marx once remarked, Age is not a particularly interesting subject. Anyone can get old. All you have to do is live long enough.
We can think of aging as marking time, such as the number of birthdays weve celebrated. Aging can also be thought about in terms of functioning. This mindset has more to do with what a person can accomplish or do on a daily basis.
People also can think about age subjectively that is, in terms of how old someone feels as opposed to how many birthdays theyve celebrated.