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Why do identical twins tend to have more similar life spans than other siblings?

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primates — aging Primates are among the longest-lived groups of mammals.

Identical twins tend to have more similar life spans than other siblings primarily because they are monozygotic, meaning they share the same genotype.21

The genetic theory of aging suggests that an organism's life span is, in part, genetically determined. Because identical twins possess the same genetic makeup, they share the same inherited predispositions for longevity and susceptibility to major age-related diseases, such as cancer and coronary heart disease. In contrast, fraternal twins and ordinary siblings are genetically different, which leads to greater variation in their biological traits and life spans.123

While environmental factors also influence how long an individual lives, the high degree of genetic similarity between identical twins results in a closer correlation in their life spans compared to non-twin siblings.21