Is there any source that gives a pixie's life span? Do they even keep track, or are they too naked and carefree to keep track of birthdays? If we don't know specifics, do we at least have a general idea of whether they live longer or shorter than humans? Do they age, or do they keep looking youthful until their life ends and they suffer Vanishment? Sorry if it's been covered already, but I didn't find the answer with a search.
EDIT: Also, do they speak their native language in their tribes, or are there some tribes that speak a human language only?