Diplosian

The Diplosians were a race of humanoids native to Diplos. They looked similar to humans, but had silvery skin, an unusual biochemistry and an allergy to citric acid.

Cessair of Diplos lived for over four millennia, though this may have been a result of her access to the Third Segment of the Key to Time, rather than a species-specific characteristic. (DW: The Stones of Blood)