A slow heart rate plays a major role in life expectancy for example,
The smallest known mammal the Etruscan shrew has a heart rate of 1,500 BPM and a lifespan of 2 years.
The largest land mammal Elephants have a heart rate of 30 BPM and a lifespan of 80 years
Tortoise have a heart rate of 10 BPM and a lifespan of 180 years
Bowhead Whales have a heart rate of 8 BPM and a lifespan of 211 years
Greenland sharks have a heart rate of 4-65 BPM and a lifespan of 392 years
Humans, with a mean heart rate of 70 b.p.m. and a life expectancy of 80 years, are an exception to the relationship between heart rate and life expectancy shown in animals , as their life expectancy is higher than that predicted by their heart rate. It has been estimated that a decrease in heart rate from 70 to 60 b.p.m. would further increase life expectancy from 80 to 93.3 years in humans.
Studies also show that restricting food intake in mice and monkeys can increase their lifespan up to 30-45%
Other factors that influence life expectancy is a healthy immune system and a good quality life.
In order for your elves to live up to 250-270 years they must have a slow heart rate around 15-20 BPM , They would only consume a small portion of food once a day and should have a superhuman immune system free from diseases and stress.