About animals like humans:

If we don't use muscles they get atrophied, so use or lose.
The cells need nutrition they need to eat, but they need exactly what they need, not too little nor too much.
but they can handle, at least for a time too little and or too much.
If too much, then the body gets older quicker, waste accumulates in the tissues, I think, when cells multiply and or get replaced very small errors are made and those small errors accumulate, ergo we get old, waste accumulation in the tissues and errors, the errors might not happen just because of the accumulation of wastes in the tissues as time goes by, there might also be other reasons.
Being alive and using your body does cause breakdown, the body rebuilds itself little by little, the body that we have right now is not the same that we had years ago.
Looks the same or older, but the atoms and cells that we had were replaced.
Why do we look older instead of younger if the body replaces itself all of the time?
It replaces itself with very tiny small mistakes that stay, accumulate and get worse in time.
Failures (errors) in the reproduction of the cells not only stay, but compound and get worse.
A cell needs to have exactly the nutrition that it needs and no more, over-eating makes us older quicker.
Eating the wrong kind of food also makes us older quicker.
We are not going to stay here very long anyway no matter what we eat and how much of it, but maybe we should not be in such a hurry to go.
So what we eat and how much can hurt the body.
What we drink and how much can hurt the body.
What we breathe and how much can hurt the body.
What our body or skin comes in contact with can hurt us.
Trauma to the body can hurt us.
What does Dr Clark said that the cause of disease is?
Parasites, toxins, pollutants and microorganisms that invade or come in contact with us.
Not getting any or not getting enough of the right nutrients can make us sick.
Getting too much nutrients can also make us sick.

The body recovers of some things up to a point and not 100%.

Residual or left-over damage accumulates.

Does thought and feelings (the mind) of a person interferes with the right replication of body tissues (cells)?

It is anybodies guess, but it might be so.

Is there a state of mind that might help the body? Again, it is anybodies guess, but it might be so.

The body seems to take care of itself at another mind level or there might be another mind level that takes care of the body, a level of which we are not aware of and don't have control over.

There is a problem somewhere as there are recovery and replication errors and there should not be.

Mythology tells us of beings that always ate and drank exactly the same food, a food that was exactly what their bodies needed in order for them to be able to live a very long time, so long that the rest of the people believed  them to be immortals, as they themselves would get old and die long before those other beings did.

So much for the theory that we should eat some of everything, instead we should eat only exactly that which we really need, that is only the nutrients that we really need.

The problem is that we really don't know 100% for sure what it is that we really need and how to get it.

So we eat a lot of things and hope that the body will take from there what we need, it seems to be so, more or less, but it is not quite 100% right.

There might also be a kind of code in us that restricts and or prevents us from living longer.

But in general that code should allow us to live at least or an average of 120 years.

That is if we have 1000 persons and count all the years that they lived before they died and devide those years by 1000 we should get about or close to 120 years most of the time or more often than not, we should get an average of 120 years, because some people should live a little more than 120 years and some a little less than 120 years.

That is not happening at all, so there is something wrong.