Getting old is a natural part of life. No matter how much we try, we cannot escape aging. However, science and medicine have helped us slow down the process, allowing humans to live longer than ever before. Today, the average global lifespan is over 70 years, a significant improvement compared to 1950, when it was just 45 years. While we can credit medical advancements for our longer lives, at what point do we stop growing and start aging?

The process of aging begins after we pass sexual maturity, typically in our late 20s. This biological process is called senescence, which means “the process of growing old.” Once we reach adulthood, our bodies become less efficient at repairing damage and maintaining our biological functions. This is not accidental—it's the way our species has evolved.

Think of the human body like a machine: the better it is maintained, the longer it lasts. Our body needs good nutrition, exercise, and proper care to function well for a long time. Scientists believe that aging happens simply because evolution has not prioritized extreme longevity for survival.

Aging in Other Species

Humans are not alone in experiencing aging. Many other species go through a similar life cycle, but some creatures age very differently. Cold-blooded animals like certain reptiles and amphibians maintain their physical health and reproductive abilities for much longer than humans.

Some species experience negligible senescence, meaning they show almost no signs of aging. These creatures, like certain types of turtles and fish, often die from external factors like predators or environmental disasters rather than from aging itself. Scientists study these species to understand how aging works and whether humans could benefit from similar biological mechanisms.

Cellular Aging

We recognize aging in humans through physical signs like wrinkles, joint pain, and gray hair. But aging also happens at a microscopic level, within our cells. The human body contains over 37 trillion cells, and each one has its own life cycle that affects how we age overall.

Every human cell has a limit on how many times it can divide, known as the Hayflick limit. This concept was discovered by scientist Leonard Hayflick, who found that normal human cells can divide approximately 40 to 60 times before they reach their limit.

One of the reasons for this limit is the presence of telomeres, protective caps at the ends of our DNA strands. Each time a cell divides, these telomeres become shorter. Eventually, they become too short to protect the DNA, and the cell can no longer function properly.

When a cell reaches the end of its life, it undergoes a self-destruction process called apoptosis. This process ensures that damaged or non-functional cells are removed from the body. However, when apoptosis fails, the affected cells become senescent, also known as "zombie cells." These cells remain alive but can no longer perform their normal functions or divide.

Over time, these zombie cells accumulate, leading to inflammation and age-related diseases like heart disease, cancer, and dementia. They also weaken surrounding tissues and contribute to degenerative disorders.

How Long Can Humans Live?

Is there a maximum limit to human life? A 2018 study found that while we can slow down aging, there seems to be a point where the risk of death stabilizes. The study, conducted at Sapienza University of Rome, examined over 3,800 Italians aged 105 and older. Researchers found that while the risk of death increases as we age, after reaching 105, it plateaus.

For example, the risk of dying in your 50s is significantly higher than in your 30s. But the study found that the probability of living from age 106 to 107 was about the same as from age 111 to 112. This suggests that there may be a biological ceiling to aging, though the exact reasons are still unclear.

Visible Signs of Aging

One of the most noticeable signs of aging is gray hair. Contrary to common belief, hair does not "turn" gray—it simply stops producing color. Hair color is determined by a pigment called melanin, which is also responsible for skin tone. As we age, the melanin-producing cells in hair follicles gradually stop working, leading to gray hair.

On average, people start to see their first gray hairs in their 30s. By age 50, about 50% of people have at least some gray hair. However, genetics play a major role—some individuals go gray much earlier or later than others.

The loss of melanin does not only affect hair. Melanocyte cells, which produce melanin in the skin, decrease by 8–20% per decade after age 30. This is why older individuals often have paler skin and are more prone to sun damage.

Another key factor in skin aging is the loss of collagen and elastin. These proteins keep the skin firm and smooth. After the age of 20, our bodies produce about 1% less collagen per year, leading to thinner skin and wrinkles.

Interestingly, some body parts continue to grow even in old age. Studies from Milan University have found that the total surface area of a person’s nose at age 65 to 80 is about 15% larger than when they were 18 to 30. This happens because cartilage keeps growing, though it becomes thicker and less flexible.

Why Do Some People Age Faster Than Others?

Aging affects everyone differently. Some people start getting gray hair in their 20s, while others don’t see their first wrinkles until their 50s. Why is this?

Our aging process is influenced by both genetics and lifestyle factors. Some people inherit genes that slow down aging, while others may have genetic factors that accelerate it. However, environment and lifestyle choices also play a big role.

A Duke University study examined how people age at a cellular level. Researchers studied 1,000 participants at ages 26, 32, and 38, measuring their metabolism, telomere length, and other aging markers.

Most participants’ biological age matched their actual age, but some aged much faster or slower than others. One participant had a biological age of 28, meaning they barely aged during the study, while another had a biological age of 61, meaning they aged three times faster than normal.

Factors like diet, exercise, sleep, and stress management can significantly impact how quickly or slowly someone ages. For example, chronic stress accelerates aging by increasing inflammation in the body. On the other hand, habits like regular physical activity and a healthy diet can slow down the aging process.

Practical Tips for Healthy Aging

• Eat a Balanced Diet: Focus on nutrient-rich foods like fruits, vegetables, whole grains, and healthy fats. Antioxidant-rich foods help combat cell damage.
• Stay Active: Regular exercise helps maintain muscle mass, bone density, and cardiovascular health.
• Get Enough Sleep: Poor sleep accelerates aging and increases the risk of diseases like dementia.
• Manage Stress: Chronic stress contributes to inflammation and premature aging.
• Protect Your Skin: Use sunscreen to prevent premature wrinkles and sun damage.
• Avoid Smoking and Excessive Alcohol: Both can speed up the aging process and contribute to disease.

Conclusion

Aging is an unavoidable part of life, but how we age is influenced by both genetics and lifestyle choices. While we cannot stop aging completely, we can slow down the process by taking care of our bodies and minds. By understanding the science of aging and making healthy choices, we can enjoy a longer, healthier, and more fulfilling life.