When we are young we fall more while learning to walk, run, ride bikes and so on, so our bones have to be stronger, and if the energy was not there we would not walk, run or even crawl. It is due to the energy we learn to walk and run. If our energy were the same at 90 as 9 we would break more bones and suffer more. That is not all there is to it either. Ok, I lost you there.
Most people make higher wages later in life.
In our 40's, 50's and 60's we seem to make more money than our 20's or 30's. And when you were the most free was late teens early 20's. When you first fell in love and it was perfect, for most that was in their 20's with some in their 30's. I think now you are getting the picture. But if not, I will help you.