Final answer:
Life expectancy measures are likely to underestimate the actual number of years someone will live due to various factors such as personal choices and access to healthcare.
Step-by-step explanation:
Life expectancy is just an average, and many people outlive the life expectancy value for their year of birth and gender. In fact, by the year 2050, a projected half a million Americans will be at least 100 years old.
Factors that can affect life expectancy include personal preferences that might affect health and longevity, such as diet, exercise, and risky behavior, as well as access to healthcare and annual check-ups.