At what point does 'growing towards adult-hood' change to 'growing older'?

I guess it's around 21 years of age.



This seems to be the point at which our development moves from one of growth, improvement and renewal to the inevitable gradual decline and decay into 'old age'.



So what 'switch is pushed at this point in our DNA?



What changes us from a blossoming flower, to a shriveling weed?



Or is the truth that we simply don't know? That this is the holy-grail the human race has searched for for centuries?



Also, does this decay-mechanism play an important part in evolution. It seems to me that the faster an organism dies after reproducing, then the better, as the next generation always presents the possibility it may produce an evolutionary 'jump', that will greatly benefit the species?



As an example, small songbirds with a life-span of around 3 years, rarely die of cancer, yet it is a common killer anongst humans.



In forwarding medical research therefore, are we in conflict with the natural order of things?

At what point does 'growing towards adult-hood' change to 'growing older'?
You actually have asked a pretty good question. I'll try to add a few scientific facts to the discussion. You have to think of aging and "growing toward adulthood" as two separate processes. The first is happening from our first cell division as zygotes all the way to our last. The second occurs so that we can achieve the major evolutionary goal of life, to reproduce.



All of our cells begin to age all the way back at zygote formation. Senescence is the scientific term for aging, and on the cellular level, we age when sections of our DNA called telomeres shorten and eventually halt DNA replication, and thus cell division. When cells stop reproducing, that curbs many functions necessary for survival, and leads to either infection, or organ failure, and ultimately death. This process doesn't "start" happening at 21, or 51 or 81. It "starts" happening when we are made up of just one single cell.



The fact that we are living longer primarily means that we are keeping ourselves less exposed to the risks that aging makes us vulnerable to. We understand how to keep our environments sanitary, and how to keep ourselves safe from dangerous microbes. We know how to maximize our health with vitamins and nutrition and exercise.



On the other hand, talking about "growing toward adulthood", we need to look at the evolutionary purpose of our existence; to survive, then reproduce. We have evolved so that it takes 14-18 years for our bodies to develop the ability to reproduce (i.e. puberty).



This has Darwinian significance in that it means reproducing around this age gives offspring the best chance of survival. And we can deduce a logical reason for this. Reproduction before this point probably means that the parents were unable to protect their offspring. Reproduction after this point might mean that there is a risk of mutation in germ cells (which is still the case today).



So, you need to look at these two processes as separate, but concurrent. Only the "growth" part of it stops somewhere in the first 20 or so years of our lives. Aging occurs throughout our lives.
Reply:When you have so many responsibilities that you no longer want to deal with them. I would say around 30.
Reply:When a broad mind and a narrow waist change places............
Reply:My 85 year old friend attended his fiftieth high school class reunion and turned to me and said in a quiet voice, "Who are all these old people - ?"



My role model, by the way, is that old guy in the commercial in his eighties who water skis on his bare feet with the tow rope clenched between his teeth. I want to be like him when I get to be eighty!
Reply:There is an extended period that is neither "growing toward adulthood" nor "growing older," but simply ordinary living. This is highly variable among individuals, and difficult to measure.



The end of "growing up" is usually given as age 22, which is when most people have reached their maximum height. It's when the zits fade away.



The onset of growing older depends on what is important to you. For most people it is when you notice that you have gone 24 hours without imagining having sex with anybody. In modern American society this is usually about age 40 to 45.



The reason for this is that for most people, sexual vitality is the clearest--and the most treasured--yardstick of vitality in general. "Growing Older" is by far the longest of the three parts of life. And many of us who are well into that period would hardly be properly referred to as shrivelling weeds.



And the answer to the last part of your question, of course, is "certainly not." The natural order of things has a different effect on people from what it has on songbirds.



Blessed be...