Ages? Stages? Behaviors?

How is it that our lifespan gets defined?

We used to speak of childhood, adolescence and adulthood. Now we have prenatal, early postnatal, postnatal, early and later infancy, early and later childhood, prepuberty, puberty, adolescence, young adulthood, middle adulthood, etc., etc.

How old are you? And - which stage/label fits you? Can we be in a few categories simultaneously?

What are ages? Those are the definitions by years or decades. You are a child, a teen, an adult. But then oops it gets odd...Are the 20's,30's and 40's similar? What about 80's and 90's?

What are stages? Usually these are certain times in life when "most" people do "something." For example, we can speak of physical development and say that most humans walk at about one year so we can talk about a walking stage or a talking stage.

But what happens when we go into areas like higher education? marriage? childbirth? careers? In the "old days" of psychology, "most" adolescents were in high school and many late teens early 20's were in college or in their career. Marriage was something that happened and in your 20's as was the birth of your 1st child.

Now we have people of all ages finishing high school and starting college. Careers are not always started in your 20's and retirement is not always in your 50's or 60's. Women are having babies into their 40's and even 50's.

People in their 80's are still out there skiing. In the ski areas nearest me, one gets a free season pass from age 72 on and recently I met an 82 year old when I went skiing. Can one describe that person as "old?" In one sense, the number, yes, but in another sense of agility and activity, no. So what is it that defines us?
Stage? Age? or Behavior?

How old are you? Here's an interesting questionnaire: http://www.realage.com