Lifespans are often determined by skill when adventuring.
Natural Lifespans:
Humans should be self-explanatory.
Elves live hundreds of years.
Dwarves live hundreds of years, but not nearly as long as elves. (300 is absolute max)
Half-Elves live about 200 years or so. Human blood makes them age faster than elves, but slower than humans.
Gnomes, halflings, half-orcs: Don't know. Likely similar to human lifespans.