Why ?

I must pose this question that is floating around in all that EMPTY space inside my head...
WHY ?

The question is why? it is not a profound question like --- Why are we here?
Or a complex question, like ---- Why do some people believe in a higher being, while others seem quite content without that in their lives?

My question is simple. Why.... Why is it that when we are young,( say 21 and in college) and have very few TRUE responsibilities ....WHY is it that... then...we have the ability to move a mile a minute, we can stay up until the wee hours of the morning just hanging out, we can function on VERY little or NO sleep at all......and still seem to be happy, and productive....

Meanwhile, here in the 40's(my new age category), I can't seem to get anything accomplished.
I have mounds of laundry that seems to reproduce every time I turn my head. I am constantly in the car - picking up or dropping off a child to school or activities.... I feel like the meals that must be prepared come every 15 minutes, it has been AGES since I sat down to scrapbook or do something that I enjoy..... and... well, I can't seem to keep my eyes open past 9:00 no matter how hard I try!!!
So the question is WHY ? It doesn't seem fair that when we have the energy and stamina.... we don't really need it....and when we need it....well we don't really have it!!!

Not complaining...really....just pondering the question....WHY?