The brain ages first, and only then the body. Whatever is not used in the body ages. Physiologists will describe many causes leading to aging of the body, or more precisely, of the brain. Here are some of them, but below I will describe my own view of this process.
Scientists identify several causes of brain aging. First, the accumulation of toxic substances in brain cells, which leads to their reduced activity and death. Second, deterioration of blood supply to the brain, causing cells to suffer from oxygen starvation. Brain aging is also associated with a decrease in the number of neurons and the connections between them. So say the scientists.
Now let's think together. As we accumulate life experience — namely after the age of 25 — we begin to think rationally. We begin to economize on our mental and physical energy. How do we think? Why memorize a phone number if there is an electronic notebook? Why calculate how much groceries cost if there is a calculator and the cash register will count everything anyway? Why go outside in bad weather? Why ski or skate? And why go for an evening walk at all if you can sit with your phone or watch a movie? Do you follow my logic? The older we get, the more rational we become. We economize on physical and mental activity.
What is the result? Whatever is not used in the body degrades successfully. That is, the body ages in response to our laziness — not the other way around.
Interesting? Read on. Let's break this down in detail.

Physical labor also plays an important role in maintaining health and longevity. I won't tell you that physical activity supports the cardiovascular system — you know that perfectly well without me. Any exercise is the ability to force yourself out of your comfort zone. It is willpower. It is a positive mindset. If you went outside for exercise or just a walk — you have already won. If you go outside regularly, in any weather — you are a winner squared.
It is important to note that exercise is also work for the brain. By doing the simplest physical exercises, you engage attention and movement coordination. All of this is work of the brain. And I have already written that the brain ages first, and only after that the body.

I have been working as a geriatrician in a nursing home for about 10 years, studying people who have preserved clear thinking despite advanced age.
Just yesterday, August 23, 2025, I spoke with an 89-year-old woman in the nursing home. I have known her for about 5 years. All these years she has been reading books or solving crosswords. Her speech is good and she is fully adequate. She is fully aware of what is happening around her. There is no trace of dementia.
Elderly people who maintain active mental activity usually have a healthier and longer lifespan. Mental work helps reduce the risk of neurodegenerative diseases such as Alzheimer's. Research shows that regular mental activity stimulates the brain, promotes the formation of new neural connections, and improves cognitive function. So what mental activity can be offered to a person over 60?

• Reading any books. Even a prayer book.
• Solving crossword puzzles. This is a very powerful brain workout.
• Memorizing the phone numbers of close relatives.
• Memorizing the lyrics of favorite songs.
• Singing. Yes, yes, don't be surprised. Singing favorite songs engages a large number of brain functions — speech, memory, and hearing.

An important aspect of longevity is also having responsibilities and work that give life meaning and direction. Any geriatrician knows: as soon as you retire, all responsibilities disappear. I sleep as much as I want. I get up when I want. Any geriatrician knows that as soon as a person retires, they fall apart.
I will say more. When even a young person lives without a routine and works on a free schedule, they degrade before your eyes. Having clearly defined responsibilities with set times mobilizes you and keeps you in shape. As long as a person works and has responsibilities, they hardly age. That is why I recommend that families with elderly relatives keep them busy and give them responsibilities. And not arbitrarily, but clearly by time. For example, every other day from 2 to 4 p.m., dust and sweep the house.