How do you think 26 out of 100 dead before 18 months old will affect "average life expectancy"?

Here are the top 20 causes of death in the early 19th century:

1. Tuberculosis
2. Pneumonia
3. Cholera
4. Typhoid fever
5. Influenza
6. Diphtheria
7. Dysentery
8. Measles
9. Smallpox
10. Malaria
11. Scarlet fever
12. Yellow fever
13. Typhus
14. Cholera infantum (diarrheal disease in infants)
15. Childbirth-related complications (for women)
16. Accidents and injuries (workplace accidents, transportation accidents, etc.)
17. Malnutrition
18. Respiratory diseases (bronchitis, asthma, etc.)
19. Syphilis
20. Rheumatic fever

Several important points above the above:

1. You will not die of any of them (except for an accident/injury).

2. These deaths were mostly evenly distributed throughout one's lives. Meaning you were just as likely to die from say Pneumonia, Cholera, Typhoid fever at 5 years old as you were at 50 years old.

Modern causes of death - Heart Disease, Cancer, Stroke, etc... - are primarily concentrated among older people - above 50 or even above 60 year old.

These huge percentages of early deaths in the past from various causes brought an average life expectancy in the past dramatically lower.

But since we are not going to die of any of the top reasons people used to die of in the past, average life expectancy statistics are completely irrelevant to us.

The only fact that matters to us is that a very significant percentage of people in the past lived till their 90s or even 100+ years old, and none of them had heart disease, cancer, or diabetes.

Below is the Mortality data (top causes of death) from the mid 18th century. It proves much of the same:

Infectious Diseases:
Smallpox
Typhus
Measles
Tuberculosis
Influenza

Childhood Diseases:
Infant mortality due to various causes
Lack of prenatal care and complications during childbirth

Malnutrition and Poor Nutrition:
Famine and food scarcity
Lack of access to nutritious food

Injuries and Accidents:
Workplace accidents
Accidental injuries
Lack of proper medical care for injuries

War and Violence:
Deaths related to wars and conflicts
Homicides and violence

Poor Sanitation and Hygiene:
Contaminated water sources
Lack of proper sewage systems
Spread of waterborne diseases

Epidemics and Pandemics:
Cholera outbreaks
Plague

Chronic obstructive pulmonary disease (COPD)
Pneumonia

Occupational Hazards:
Hazards related to various professions, such as mining and construction