World building is much easier if there aren't 2000-year olds about. Instead of doing research on mystical ruins, there are people alive who knows. If they don't know, their grandfather told them and that grandfather lived 5000 years ago. If an elf can be 2000 years old and it's immune to disease (Tolkien- style) and keeps away from violence, you could cover Earth from the city of Ur to today within the lifetime of four elves. History would be a very different science than it is today.
That's my theory why the races live shorter.
For my own games, I have traditionally said that elves live forever as long as they don't change. The MM- elf is one of those who don't. They live their lives like they always have done, they don't learn anything new. When an elf decides that he wants to learn and grow and experience things, he gets the taint that humanity suffers from. That elf will live a short time, like a human.
That's my theory why the races live shorter.
For my own games, I have traditionally said that elves live forever as long as they don't change. The MM- elf is one of those who don't. They live their lives like they always have done, they don't learn anything new. When an elf decides that he wants to learn and grow and experience things, he gets the taint that humanity suffers from. That elf will live a short time, like a human.