I keep asking myself the same question everytime I get out on that tennis court these days
:-)

Imagine if you will, a Human cell as a party balloon.

When you're young it's all big and tight.

The space around each cell is also clear and clean.

Light energy from the body's fuel can get into the mitochondrion in the centre of the cell and create energy. You fell "young" and vibrant.

Now, think of the same balloon after it's sat behind the sofa for a few weeks after the party.

It's shrivelled down a bit, right?

That is the same as human cells after a lifetime ( 60, 70 or 80 years) depending on the levels of "abuse" they have had.

Now it's more difficult for light and energy to get into the cell. The gaps between the cells have also gone from clear liquid to cloudiness.

What energy is in the cells struggles to get to where it's supposed to go.

Age.

Funny thing.

Not enough sleep. Too much getting up in the middle of the night to have a wee. Old people tend to get up very early so tend to flake out by 8PM.